Fabrication of touch, handwriting and fingerprint sensor

ABSTRACT

Fabrication methods for combined sensor devices include substantially transparent substrates and materials to increase the optical performance of underlying displays. A substantially transparent elastomeric material may be disposed between the substantially transparent substrates. Some fabrication processes utilize flexible substrates for at least a portion of the sensor device, and lend themselves to roll-to-roll processing for low cost.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/394,054, entitled “COMBINATION TOUCH, HANDWRITING AND FINGERPRINTSENSOR” (Attorney Docket No. QUALP045P/102908P1) and filed on Oct. 18,2010, which is hereby incorporated by reference and for all purposes.This application is related to U.S. patent application Ser. No. ______,entitled “COMBINATION TOUCH, HANDWRITING AND FINGERPRINT SENSOR”(Attorney Docket No. QUALP045A/102908U1) and filed on Oct. 11, 2011, toU.S. patent application Ser. No. ______, entitled “TOUCH, HANDWRITINGAND FINGERPRINT SENSOR WITH ELASTOMERIC SPACER LAYER” (Attorney DocketNo. QUALP045C/102908U3) and filed on Oct. 11, 2011, to U.S. patentapplication Ser. No. ______, entitled “TOUCH SENSOR WITH FORCE-ACTUATEDSWITCHED CAPACITOR” (Attorney Docket No. QUALP045D/102908U4) and filedon Oct. 11, 2011, to U.S. patent application Ser. No. ______, entitled“WRAPAROUND ASSEMBLY FOR COMBINATION TOUCH, HANDWRITING AND FINGERPRINTSENSOR” (Attorney Docket No. QUALP045E/102908U5) and filed on Oct. 11,2011, to U.S. patent application Ser. No. ______, entitled“MULTIFUNCTIONAL INPUT DEVICE FOR AUTHENTICATION AND SECURITYAPPLICATIONS” (Attorney Docket No. QUALP045F/102908U6) and filed on Oct.11, 2011, to U.S. patent application Ser. No. ______, entitled“CONTROLLER ARCHITECTURE FOR COMBINATION TOUCH, HANDWRITING ANDFINGERPRINT SENSOR” (Attorney Docket No. QUALP045G/102908U7) and filedon Oct. 11, 2011, all of which are hereby incorporated by reference andfor all purposes.

TECHNICAL FIELD

This disclosure relates to display devices, including but not limited todisplay devices that incorporate multifunctional touch screens.

DESCRIPTION OF THE RELATED TECHNOLOGY

Electromechanical systems (EMS) include devices having electrical andmechanical elements, actuators, transducers, sensors, optical components(including mirrors) and electronics. Electromechanical systems can bemanufactured at a variety of scales including, but not limited to,microscales and nanoscales. For example, microelectromechanical systems(MEMS) devices can include structures having sizes ranging from about amicron to hundreds of microns or more. Nanoelectromechanical systems(NEMS) devices can include structures having sizes smaller than a micronincluding, for example, sizes smaller than several hundred nanometers.Electromechanical elements may be created using deposition, etching,lithography, and/or other micromachining processes that etch away partsof substrates and/or deposited material layers, or that add layers toform electrical and electromechanical devices.

One type of EMS device is called an interferometric modulator (IMOD). Asused herein, the term interferometric modulator or interferometric lightmodulator refers to a device that selectively absorbs and/or reflectslight using the principles of optical interference. In someimplementations, an interferometric modulator may include a pair ofconductive plates, one or both of which may be transparent and/orreflective, wholly or in part, and capable of relative motion uponapplication of an appropriate electrical signal. In an implementation,one plate may include a stationary layer deposited on a substrate andthe other plate may include a reflective membrane separated from thestationary layer by an air gap. The position of one plate in relation toanother can change the optical interference of light incident on theinterferometric modulator. Interferometric modulator devices have a widerange of applications, and are anticipated to be used in improvingexisting products and creating new products, especially those withdisplay capabilities.

The increased use of touch screens in handheld devices causes increasedcomplexity and cost for modules that now include the display, the touchpanel and a cover glass. Each layer in the device adds thickness andrequires costly glass-to-glass bonding solutions for attachment to theneighboring substrates. These problems can be further exacerbated forreflective displays when a frontlight also needs to be integrated,adding to the thickness and cost of the module.

SUMMARY

The systems, methods and devices of the disclosure each have severalinnovative aspects, no single one of which is solely responsible for thedesirable attributes disclosed herein. Some implementations describedherein provide a combined sensor device that combines aspects ofcapacitive and resistive technologies for touch sensing, handwritinginput and fingerprint imaging. Some such implementations provide a touchsensor that combines capacitive and resistive technologies to enable amulti-feature user input sensor overlaid on a display.

In some such implementations, a cover glass apparatus of a consumerdevice such as a cell phone, an e-reader, or a tablet computer servesadditionally as part of a combined sensor device having a single ormulti-touch sensor, a handwriting or stylus input device, and/or afingerprint sensor. The cover glass apparatus may include 2, 3 or morelayers. The substrates used to form a cover glass apparatus may beformed of various suitable substantially transparent materials, such asactual glass, plastic, polymer, etc. Such a cover glass apparatus withtouch, handwriting and/or fingerprint detection capability may, forexample, be overlaid on a display.

One innovative aspect of the subject matter described in this disclosurecan be implemented in a method that may involve depositing a first layerof substantially transparent conductive material on a firstsubstantially transparent substrate. The depositing process may involveforming a first plurality of substantially transparent electrodes in afirst region of the first substrate and forming a second plurality ofsubstantially transparent electrodes in a second region of the firstsubstrate. The method may involve forming a layer of resistive materialon the first layer of substantially transparent conductive material. Theforming process may include forming a first plurality of resistors onsome, but not all, of the first plurality of electrodes and forming asecond plurality of resistors on the second plurality of electrodes.

The method may involve depositing a second layer of substantiallytransparent conductive material on a second substantially transparentand flexible substrate. Depositing the second layer may involve forminga third plurality of substantially transparent electrodes in a firstregion of the second substrate and forming a fourth plurality ofsubstantially transparent electrodes in a second region of the secondsubstrate with a pitch that is substantially the same as that of thesecond plurality of electrodes. The method may involve forming asubstantially transparent elastomeric material in the first region ofthe first substrate and attaching the second substrate to theelastomeric material.

The method may involve forming a force-sensitive resistor materialbetween the second plurality of electrodes and the fourth plurality ofelectrodes and/or between the first plurality of electrodes and thethird plurality of electrodes. An index of refraction of the firstsubstrate may substantially match an index of refraction of theelastomeric material. An index of refraction of the elastomeric materialmay substantially match an index of refraction of the second substrate.The modulus of elasticity of the elastomeric material may besubstantially lower than a modulus of elasticity of the secondsubstrate.

The method may involve forming the elastomeric material on the firstelectrodes having the first plurality of resistors deposited thereon.Forming the elastomeric material on the first electrodes having thefirst plurality of resistors deposited thereon may involve forming theelastomeric material on the first electrodes not having the firstplurality of resistors deposited thereon and then removing theelastomeric material from the first electrodes having the firstplurality of resistors deposited thereon. The removing process mayinvolve removing the elastomeric material from less than 5% of the firstregion. However, in some implementations, the method may involve formingthe elastomeric material on the first electrodes not having the firstplurality of resistors deposited thereon and not removing theelastomeric material from the first electrodes having the firstplurality of resistors deposited thereon.

The method may involve applying an adhesive layer to the elastomericmaterial, but not to the resistive material, prior to the attachingprocess. The method may involve attaching the first substantiallytransparent substrate to a display device. At least some aspects of themethod (such as the depositing) may involve a roll-to-roll manufacturingprocess.

The method may involve configuring a sensor control system forcommunication with the first and third pluralities of substantiallytransparent electrodes and/or with the second and fourth pluralities ofsubstantially transparent electrodes. The method may involve configuringthe sensor control system for processing fingerprint sensor dataaccording to electrical signals received from the second and fourthpluralities of substantially transparent electrodes. The method mayinvolve configuring the sensor control system for communication with aprocessor of a display device.

The method may involve configuring the sensor control system forprocessing handwriting and touch sensor data according to electricalsignals received from the first and third pluralities of substantiallytransparent electrodes. Configuring the sensor control system forprocessing handwriting and touch sensor data may involve configuring thesensor control system for projected capacitive touch sensing.Configuring the sensor control system for processing handwriting andtouch sensor data may involve configuring the sensor control system forresistive handwriting sensing. Configuring the sensor control system forprocessing handwriting and touch sensor data may involve configuring thesensor control system for capacitive handwriting sensing.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented in an alternative method that may involvedepositing a first layer of substantially transparent conductivematerial on a first substantially transparent substrate. Depositing thefirst layer may involve forming a first plurality of substantiallytransparent electrodes in a first region of the first substrate andforming a second plurality of substantially transparent electrodes in asecond region of the first substrate. In some implementations, thesecond plurality of electrodes may be spaced more closely than the firstplurality of electrodes.

The method may involve forming a layer of resistive material on thefirst layer of substantially transparent conductive material. Theforming may include forming a first plurality of resistors on some, butnot all, of the first plurality of electrodes and forming a secondplurality of resistors on the second plurality of electrodes.

The method may involve depositing a second layer of substantiallytransparent conductive material on a second substantially transparentand flexible substrate. Depositing the second layer may involve forminga third plurality of substantially transparent electrodes in a firstregion of the second substrate and forming a fourth plurality ofsubstantially transparent electrodes in a second region of the secondsubstrate with a pitch that is substantially the same as that of thesecond plurality of electrodes.

The method may involve forming a substantially transparent elastomericmaterial in the first region of the first substrate and attaching thesecond substrate to the elastomeric material. An index of refraction ofthe first substrate and/or the second substrate may substantially matchan index of refraction of the elastomeric material. The method mayinvolve forming substantially transparent and force-sensitive resistormaterial extending from the second plurality of electrodes to the fourthplurality of electrodes.

A modulus of elasticity of the elastomeric material may be substantiallylower than a modulus of elasticity of the second substrate. For example,the modulus of elasticity of the elastomeric material may be betweenabout 0.5 and 50 megapascals and the modulus of elasticity of the secondsubstrate may be between about 0.5 and 5.0 gigapascals.

Forming the substantially transparent elastomeric material may involvesubstantially filling a space between only a portion of the firstplurality of electrodes and the third plurality of electrodes with theelastomeric material. Forming the substantially transparent elastomericmaterial may involve substantially filling a space between substantiallyall of the first plurality of electrodes and the third plurality ofelectrodes with the elastomeric material.

Details of one or more implementations of the subject matter describedin this specification are set forth in the accompanying drawings and thedescription below. Although the examples provided in this summary areprimarily described in terms of MEMS-based displays, the conceptsprovided herein may apply to other types of displays, such as liquidcrystal displays, organic light-emitting diode (“OLED”) displays andfield emission displays. Other features, aspects, and advantages willbecome apparent from the description, the drawings, and the claims. Notethat the relative dimensions of the following figures may not be drawnto scale.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of an isometric view depicting two adjacentpixels in a series of pixels of an interferometric modulator (IMOD)display device.

FIG. 2 shows an example of a system block diagram illustrating anelectronic device incorporating a 3×3 interferometric modulator display.

FIG. 3 shows an example of a diagram illustrating movable reflectivelayer position versus applied voltage for the interferometric modulatorof FIG. 1.

FIG. 4 shows an example of a table illustrating various states of aninterferometric modulator when various common and segment voltages areapplied.

FIG. 5A shows an example of a diagram illustrating a frame of displaydata in the 3×3 interferometric modulator display of FIG. 2.

FIG. 5B shows an example of a timing diagram for common and segmentsignals that may be used to write the frame of display data illustratedin FIG. 5A.

FIG. 6A shows an example of a partial cross-section of theinterferometric modulator display of FIG. 1.

FIGS. 6B-6E show examples of cross-sections of varying implementationsof interferometric modulators.

FIG. 7 shows an example of a flow diagram illustrating a manufacturingprocess for an interferometric modulator.

FIGS. 8A-8E show examples of cross-sectional schematic illustrations ofvarious stages in a method of making an interferometric modulator.

FIG. 9A shows an example of sensor electrodes formed on a cover glass.

FIG. 9B shows an alternative example of sensor electrodes formed on acover glass.

FIG. 10A shows an example of a cross-sectional view of a combined sensordevice.

FIGS. 10B-10D show examples of cross-sectional views of alternativecombined sensor devices.

FIGS. 11A-11D show examples of cross-sectional views of combined sensordevices having high-modulus and low-modulus compressible layers.

FIG. 12 shows an example of a device that includes a cover glass with acombination touch, handwriting and fingerprint sensor.

FIG. 13 shows an example of a top view of a force-sensitive switchimplementation.

FIG. 14 shows an example of a cross-section through a row of theforce-sensitive switch implementation shown in FIG. 13.

FIG. 15A shows an example of a circuit diagram that representscomponents of the implementation shown in FIGS. 13 and 14.

FIG. 15B shows an example of a circuit diagram that representscomponents of an alternative implementation related to FIGS. 13 and 14.

FIG. 16 shows an example of a flow diagram illustrating a manufacturingprocess for a combined sensor device.

FIGS. 17A-17D show examples of partially formed combined sensor devicesduring various stages of the manufacturing process of FIG. 16.

FIG. 18A shows an example of a block diagram that illustrates ahigh-level architecture of a combined sensor device.

FIG. 18B shows an example of a block diagram that illustrates a controlsystem for a combined sensor device.

FIG. 18C shows an example representation of physical components andtheir electrical equivalents for a sensel in a combined sensor device.

FIG. 18D shows an example of an alternative sensel of a combined sensordevice.

FIG. 18E shows an example of a schematic diagram representing equivalentcircuit components of a sensel in a combined sensor device.

FIG. 18F shows an example of an operational amplifier circuit for acombined sensor device that may be configured for handwriting or stylusmode sensing.

FIG. 18G shows an example of the operational amplifier circuit of FIG.18F configured for touch mode sensing.

FIG. 18H shows an example of an operational amplifier circuit for acombined sensor device that includes a clamp circuit.

FIG. 18I shows examples of clamp circuit transfer functions.

FIG. 18J shows an example of a circuit diagram for a clamp circuit.

FIG. 19 shows an example of a cross-section of a portion of analternative combined sensor device.

FIG. 20 shows an example of a top view of routing for a combined sensordevice.

FIG. 21A shows an example of a cross-sectional view through the combinedsensor device shown in FIG. 20.

FIG. 21B shows an example of a cross-sectional view of a wrap-aroundimplementation.

FIG. 22 shows an example of a flow diagram illustrating afingerprint-based user authentication process.

FIG. 23A shows an example of a mobile device that may be configured formaking secure commercial transactions.

FIG. 23B shows an example of using a fingerprint-secured mobile devicefor physical access applications.

FIG. 24A shows an example of a secure tablet device.

FIG. 24B shows an example of an alternative secure tablet device.

FIGS. 25A and 25B show examples of system block diagrams illustrating adisplay device that includes a combined sensor device.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

The following description is directed to certain implementations for thepurposes of describing the innovative aspects of this disclosure.However, a person having ordinary skill in the art will readilyrecognize that the teachings herein can be applied in a multitude ofdifferent ways. The described implementations may be implemented in anydevice or system that can be configured to display an image, whether inmotion (e.g., video) or stationary (e.g., still image), and whethertextual, graphical or pictorial. More particularly, it is contemplatedthat the described implementations may be included in or associated witha variety of electronic devices such as, but not limited to: mobiletelephones, multimedia Internet enabled cellular telephones, mobiletelevision receivers, wireless devices, smartphones, Bluetooth® devices,personal data assistants (PDAs), wireless electronic mail receivers,hand-held or portable computers, netbooks, notebooks, smartbooks,tablets, printers, copiers, scanners, facsimile devices, GPSreceivers/navigators, cameras, MP3 players, camcorders, game consoles,wrist watches, clocks, calculators, television monitors, flat paneldisplays, electronic reading devices (i.e., e-readers), computermonitors, auto displays (including odometer and speedometer displays,etc.), cockpit controls and/or displays, camera view displays (such asthe display of a rear view camera in a vehicle), electronic photographs,electronic billboards or signs, projectors, architectural structures,microwaves, refrigerators, stereo systems, cassette recorders orplayers, DVD players, CD players, VCRs, radios, portable memory chips,washers, dryers, washer/dryers, parking meters, packaging (such as inelectromechanical systems, microelectromechanical systems, and non-MEMSapplications), aesthetic structures (e.g., display of images on a pieceof jewelry) and a variety of EMS devices. The teachings herein also canbe used in non-display applications such as, but not limited to,electronic switching devices, radio frequency filters, sensors,accelerometers, gyroscopes, motion-sensing devices, magnetometers,inertial components for consumer electronics, parts of consumerelectronics products, varactors, liquid crystal devices, electrophoreticdevices, drive schemes, manufacturing processes and electronic testequipment. Thus, the teachings are not intended to be limited to theimplementations depicted solely in the Figures, but instead have wideapplicability as will be readily apparent to one having ordinary skillin the art.

Some implementations described herein combine novel aspects ofcapacitive and resistive technologies for touch sensing, stylusdetection for handwriting input, and fingerprint imaging. Some suchimplementations provide a combined sensor device, at least part of whichis incorporated in a cover glass apparatus that may be overlaid on orotherwise combined with a display. The cover glass apparatus may have 2,3 or more layers. In some implementations, the cover glass apparatusincludes a substantially transparent and flexible upper substrate and asubstantially transparent and relatively more rigid lower substrate. Insome such implementations, the lower substrate of the cover glassapparatus may be overlaid on a display substrate. In alternativeimplementations, the lower substrate of the cover glass apparatus may bea display substrate. For example, the lower substrate of the cover glassapparatus may be the same transparent substrate on which IMOD devicesare fabricated, as described below.

Various implementations of such sensor devices are described herein. Insome implementations, the cover glass of a display device serves as asingle or multi-touch sensor, as a handwriting (or note capture) inputdevice, and as a fingerprint sensor. Sensor functionality and resolutioncan be tailored to specific locations on the cover glass. In some suchimplementations, the area in which the fingerprint sensing elements arelocated may provide not only fingerprint detection, but also handwritingand touch functionality. In some other implementations, the fingerprintsensor may be segregated in a separate, high-resolution zone that onlyprovides fingerprint functionality. In some implementations, the sensordevice serves as a combination touch and stylus input device. Variousmethods of fabrication are described herein, as well as methods forusing a device that includes a combined sensor device.

Particular implementations of the subject matter described in thisdisclosure can be implemented to realize one or more of the followingpotential advantages. Some implementations described herein combineaspects of capacitive and resistive technologies for touch sensing,handwriting input and in some cases fingerprint imaging. Some suchimplementations provide a touch sensor that combines capacitive andresistive technologies to enable a multi-functional user input sensorthat can be overlaid on a display. Some implementations of the combinedsensor device eliminate a middle touch sensor layer that is disposedbetween the cover glass and the display glass in some conventionalprojected capacitive touch (PCT)-based devices. Accordingly, some suchimplementations can mitigate or eliminate at least some drawbacks of PCTand resistive technologies.

A hybrid PCT and digital resistive touch (DRT) implementation allows,for example, detection of a narrow stylus tip pressing onto the displaywith the DRT aspect while also allowing the detection of very lightbrushing or close hovering over the display with a finger using the PCTaspect. The sensor device can accept any form of stylus or pen input,regardless of whether it is conducting or non-conducting. Transparent oreffectively transparent force-sensitive resistors may be included withinsome or all of the sensels to improve optical and electricalperformance.

According to some implementations, the combination sensor may includetwo or more patterned layers, some of which may be on a differentsubstrate. The upper (or outer) substrate may, for example, be formed ofa plastic such as polyethylene terephthalate (PET), polyethylenenaphthalate (PEN), polyimide, or a similar material. The upper substratealso may be substantially transparent and have a substantiallytransparent conductor such as indium-tin-oxide (ITO) patterned on itsunderside. The lower substrate may be formed of a substantiallytransparent substrate material, such as glass, with another suitablematerial. The top surface of the substantially transparent substrate canbe a patterned layer of substantially transparent conductor materialsuch as ITO. In some implementations, the conductors on the underside ofthe upper substrate and the upper side of the lower substrate may bepatterned into diamond-shaped electrodes, connected as rows or columnson each of the two different layers

Some such implementations include a wrap-around configuration wherein aflexible upper substrate of the sensor device has patternedmetallization on an extended portion to allow routing of signal lines,electrical ground, and power. This flexible upper substrate may bewrapped around an edge of a relatively more rigid lower substrate of thecover glass apparatus. One or more ICs or passive components includingconnecting sockets may be mounted onto the flexible layer to reduce costand complexity. Signal lines that address sensor electrodes on the lowersubstrate may be routed and connected to corresponding patterns on theunderside of the flexible upper substrate. Such implementations have thepotential advantage of eliminating the need for a flex cable forelectrically connecting signal lines of the upper layer to integratedcircuits and/or other devices. The approach allows a bezel-lessconfiguration for some versions of the final cover glass apparatus.

Fabrication methods include predominantly transparent substrates andmaterials to increase the optical performance of underlying displays.The fabrication processes may utilize flexible substrates for at least aportion of the sensor device, and lend themselves to roll-to-rollprocessing for low cost.

Use of a compliant, elastomeric layer between upper and lower portionsof the combination sensor can increase the sensitivity to appliedpressure or force from a stylus, while increasing the lateral resolutionfor a given sensel pitch. The elastomeric material may include openregions for the inclusion of force-sensitive resistors. With carefulselection of the elastomeric and FSR materials, the loss oftransmissivity that can accompany air gaps is minimized.

An array of force-sensitive switches and local capacitors may be used toconnect the local capacitor into associated PCT detection circuitry,where each capacitor is formed with a thin dielectric layer to achieve ahigh capacitance increase when the force-sensitive switch is closed bythe pressing of a stylus or finger. The same PCT detection circuitry cantherefore be used to detect changes in mutual capacitance when touchedwith a finger (touch mode) and changes in sensel capacitance when theforce-sensitive switch is depressed (stylus or fingerprint mode).

The combined, multi-functional sensor device enables a singletouchscreen to perform additional functions such as handwriting inputand fingerprint recognition. In some implementations, these multiplefeatures allow increased security through user authentication, and allowbetter capture of handwriting and a more interactive approach to userinterfaces. A handheld mobile device such as a cell phone with thesensor device enables an array of applications, including using themobile device as a gateway for user authentication to enabletransactions and physical access; using the handwriting input functionfor signature recognition and transmittal for transaction applications;and using the handwriting input feature to automatically capture notesand other documents of students in an academic setting or employees in acorporate setting.

In some such implementations, a separate controller may be configuredfor the sensor device, or the controller may be included as part of anapplications processor. Software for handwriting, touch and fingerprintdetection may be included on one or more controllers or the applicationsprocessor. Low, medium and high resolution can be obtained with a singlesensor device by scanning a subset of the sensels, or by aggregatinglines or columns. Power consumption may be reduced by aggregating sensorpixels (or rows or columns) electrically using the controller, so thatthey perform as a low power small array until higher resolution with alarger array is needed. Power consumption may be reduced by turning offportions or all of the sensor device, turning off parts of thecontroller, or employing first-level screening at a reduced frame rate.In some such implementations, a combination PCT sensor and digitalresistive touch (DRT) sensor has a passive array of capacitors (PCT) anda passive array of resistive switches (DRT). While the touch sensor andstylus sensor systems generally use different sensing techniques, aholistic approach with a common structure saves on PCB part count,reduces area in an ASIC implementation, reduces power, and eliminatesthe need for isolation between touch and stylus subsystems.

An example of a suitable EMS or MEMS device, to which the describedimplementations may apply, is a reflective display device. Reflectivedisplay devices can incorporate interferometric modulators (IMODs) toselectively absorb and/or reflect light incident thereon usingprinciples of optical interference. IMODs can include an absorber, areflector that is movable with respect to the absorber, and an opticalresonant cavity defined between the absorber and the reflector. Thereflector can be moved to two or more different positions, which canchange the size of the optical resonant cavity and thereby affect thereflectance of the interferometric modulator. The reflectance spectrumsof IMODs can create fairly broad spectral bands which can be shiftedacross the visible wavelengths to generate different colors. Theposition of the spectral band can be adjusted by changing the thicknessof the optical resonant cavity. One way of changing the optical resonantcavity is by changing the position of the reflector.

FIG. 1 shows an example of an isometric view depicting two adjacentpixels in a series of pixels of an interferometric modulator (IMOD)display device. The IMOD display device includes one or moreinterferometric MEMS display elements. In these devices, the pixels ofthe MEMS display elements can be in either a bright or dark state. Inthe bright (“relaxed,” “open” or “on”) state, the display elementreflects a large portion of incident visible light, e.g., to a user.Conversely, in the dark (“actuated,” “closed” or “off”) state, thedisplay element reflects little incident visible light. In someimplementations, the light reflectance properties of the on and offstates may be reversed. MEMS pixels can be configured to reflectpredominantly at particular wavelengths allowing for a color display inaddition to black and white.

The IMOD display device can include a row/column array of IMODs. EachIMOD can include a pair of reflective layers, i.e., a movable reflectivelayer and a fixed partially reflective layer, positioned at a variableand controllable distance from each other to form an air gap (alsoreferred to as an optical gap or cavity). The movable reflective layermay be moved between at least two positions. In a first position, i.e.,a relaxed position, the movable reflective layer can be positioned at arelatively large distance from the fixed partially reflective layer. Ina second position, i.e., an actuated position, the movable reflectivelayer can be positioned more closely to the partially reflective layer.Incident light that reflects from the two layers can interfereconstructively or destructively depending on the position of the movablereflective layer, producing either an overall reflective ornon-reflective state for each pixel. In some implementations, the IMODmay be in a reflective state when unactuated, reflecting light withinthe visible spectrum, and may be in a dark state when unactuated,absorbing and/or destructively interfering light within the visiblerange. In some other implementations, however, an IMOD may be in a darkstate when unactuated, and in a reflective state when actuated. In someimplementations, the introduction of an applied voltage can drive thepixels to change states. In some other implementations, an appliedcharge can drive the pixels to change states.

The depicted portion of the pixel array in FIG. 1 includes two adjacentinterferometric modulators 12 (i.e., IMOD pixels). In the IMOD 12 on theleft (as illustrated), a movable reflective layer 14 is illustrated in arelaxed position at a distance (which may be predetermined based ondesign parameters) from an optical stack 16, which includes a partiallyreflective layer. The voltage V₀ applied across the IMOD 12 on the leftis insufficient to cause actuation of the movable reflective layer 14.In the IMOD 12 on the right, the movable reflective layer 14 isillustrated in an actuated position near, adjacent or touching theoptical stack 16. The voltage V_(bias) applied across the IMOD 12 on theright is sufficient to move and can maintain the movable reflectivelayer 14 in the actuated position.

In FIG. 1, the reflective properties of pixels 12 are generallyillustrated with arrows 13 indicating light incident upon the pixels 12,and light 15 reflecting from the pixel 12 on the left. A person havingordinary skill in the art will readily recognize that most of the light13 incident upon the pixels 12 may be transmitted through thetransparent substrate 20, toward the optical stack 16. A portion of thelight incident upon the optical stack 16 may be transmitted through thepartially reflective layer of the optical stack 16, and a portion willbe reflected back through the transparent substrate 20. The portion oflight 13 that is transmitted through the optical stack 16 may bereflected at the movable reflective layer 14, back toward (and through)the transparent substrate 20. Interference (constructive or destructive)between the light reflected from the partially reflective layer of theoptical stack 16 and the light reflected from the movable reflectivelayer 14 will determine the wavelength(s) of light 15 reflected from thepixel 12.

The optical stack 16 can include a single layer or several layers. Thelayer(s) can include one or more of an electrode layer, a partiallyreflective and partially transmissive layer and a transparent dielectriclayer. In some implementations, the optical stack 16 is electricallyconductive, partially transparent and partially reflective, and may befabricated, for example, by depositing one or more of the above layersonto a transparent substrate 20. The electrode layer can be formed froma variety of materials, such as various metals, for example indium tinoxide (ITO). The partially reflective layer can be formed from a varietyof materials that are partially reflective, such as various metals, suchas chromium (Cr), semiconductors, and dielectrics. The partiallyreflective layer can be formed of one or more layers of materials, andeach of the layers can be formed of a single material or a combinationof materials. In some implementations, the optical stack 16 can includea single semi-transparent thickness of metal or semiconductor whichserves as both an optical absorber and electrical conductor, whiledifferent, more electrically conductive layers or portions (e.g., of theoptical stack 16 or of other structures of the IMOD) can serve to bussignals between IMOD pixels. The optical stack 16 also can include oneor more insulating or dielectric layers covering one or more conductivelayers or an electrically conductive/optically absorptive layer.

In some implementations, the layer(s) of the optical stack 16 can bepatterned into parallel strips, and may form row electrodes in a displaydevice as described further below. As will be understood by one havingordinary skill in the art, the term “patterned” is used herein to referto masking as well as etching processes. In some implementations, ahighly conductive and reflective material, such as aluminum (Al), may beused for the movable reflective layer 14, and these strips may formcolumn electrodes in a display device. The movable reflective layer 14may be formed as a series of parallel strips of a deposited metal layeror layers (orthogonal to the row electrodes of the optical stack 16) toform columns deposited on top of posts 18 and an intervening sacrificialmaterial deposited between the posts 18. When the sacrificial materialis etched away, a defined gap 19, or optical cavity, can be formedbetween the movable reflective layer 14 and the optical stack 16. Insome implementations, the spacing between posts 18 may be approximately1-1000 um, while the gap 19 may be approximately less than 10,000Angstroms (Å).

In some implementations, each pixel of the IMOD, whether in the actuatedor relaxed state, is essentially a capacitor formed by the fixed andmoving reflective layers. When no voltage is applied, the movablereflective layer 14 remains in a mechanically relaxed state, asillustrated by the pixel 12 on the left in FIG. 1, with the gap 19between the movable reflective layer 14 and optical stack 16. However,when a potential difference, e.g., voltage, is applied to at least oneof a selected row and column, the capacitor formed at the intersectionof the row and column electrodes at the corresponding pixel becomescharged, and electrostatic forces pull the electrodes together. If theapplied voltage exceeds a threshold, the movable reflective layer 14 candeform and move near or against the optical stack 16. A dielectric layer(not shown) within the optical stack 16 may prevent shorting and controlthe separation distance between the layers 14 and 16, as illustrated bythe actuated pixel 12 on the right in FIG. 1. The behavior is the sameregardless of the polarity of the applied potential difference. Though aseries of pixels in an array may be referred to in some instances as“rows” or “columns,” a person having ordinary skill in the art willreadily understand that referring to one direction as a “row” andanother as a “column” is arbitrary. Restated, in some orientations, therows can be considered columns, and the columns considered to be rows.Furthermore, the display elements may be evenly arranged in orthogonalrows and columns (an “array”), or arranged in non-linear configurations,for example, having certain positional offsets with respect to oneanother (a “mosaic”). The terms “array” and “mosaic” may refer to eitherconfiguration. Thus, although the display is referred to as including an“array” or “mosaic,” the elements themselves need not be arrangedorthogonally to one another, or disposed in an even distribution, in anyinstance, but may include arrangements having asymmetric shapes andunevenly distributed elements.

FIG. 2 shows an example of a system block diagram illustrating anelectronic device incorporating a 3×3 interferometric modulator display.The electronic device includes a processor 21 that may be configured toexecute one or more software modules. In addition to executing anoperating system, the processor 21 may be configured to execute one ormore software applications, including a web browser, a telephoneapplication, an email program, or any other software application.

The processor 21 can be configured to communicate with an array driver22. The array driver 22 can include a row driver circuit 24 and a columndriver circuit 26 that provide signals to, e.g., a display array orpanel 30. The cross section of the IMOD display device illustrated inFIG. 1 is shown by the lines 1-1 in FIG. 2. Although FIG. 2 illustratesa 3×3 array of IMODs for the sake of clarity, the display array 30 maycontain a very large number of IMODs, and may have a different number ofIMODs in rows than in columns, and vice versa.

FIG. 3 shows an example of a diagram illustrating movable reflectivelayer position versus applied voltage for the interferometric modulatorof FIG. 1. For MEMS interferometric modulators, the row/column (i.e.,common/segment) write procedure may take advantage of a hysteresisproperty of these devices as illustrated in FIG. 3. An interferometricmodulator may require, for example, about a 10-volt potential differenceto cause the movable reflective layer, or mirror, to change from therelaxed state to the actuated state. When the voltage is reduced fromthat value, the movable reflective layer maintains its state as thevoltage drops back below, e.g., 10-volts, however, the movablereflective layer does not relax completely until the voltage drops below2-volts. Thus, a range of voltage, approximately 3 to 7-volts, as shownin FIG. 3, exists where there is a window of applied voltage withinwhich the device is stable in either the relaxed or actuated state. Thisis referred to herein as the “hysteresis window” or “stability window.”For a display array 30 having the hysteresis characteristics of FIG. 3,the row/column write procedure can be designed to address one or morerows at a time, such that during the addressing of a given row, pixelsin the addressed row that are to be actuated are exposed to a voltagedifference of about 10-volts, and pixels that are to be relaxed areexposed to a voltage difference of near zero volts. After addressing,the pixels are exposed to a steady state or bias voltage difference ofapproximately 5-volts such that they remain in the previous strobingstate. In this example, after being addressed, each pixel sees apotential difference within the “stability window” of about 3-7-volts.This hysteresis property feature enables the pixel design, e.g.,illustrated in FIG. 1, to remain stable in either an actuated or relaxedpre-existing state under the same applied voltage conditions. Since eachIMOD pixel, whether in the actuated or relaxed state, is essentially acapacitor formed by the fixed and moving reflective layers, this stablestate can be held at a steady voltage within the hysteresis windowwithout substantially consuming or losing power. Moreover, essentiallylittle or no current flows into the IMOD pixel if the applied voltagepotential remains substantially fixed.

In some implementations, a frame of an image may be created by applyingdata signals in the form of “segment” voltages along the set of columnelectrodes, in accordance with the desired change (if any) to the stateof the pixels in a given row. Each row of the array can be addressed inturn, such that the frame is written one row at a time. To write thedesired data to the pixels in a first row, segment voltagescorresponding to the desired state of the pixels in the first row can beapplied on the column electrodes, and a first row pulse in the form of aspecific “common” voltage or signal can be applied to the first rowelectrode. The set of segment voltages can then be changed to correspondto the desired change (if any) to the state of the pixels in the secondrow, and a second common voltage can be applied to the second rowelectrode. In some implementations, the pixels in the first row areunaffected by the change in the segment voltages applied along thecolumn electrodes, and remain in the state they were set to during thefirst common voltage row pulse. This process may be repeated for theentire series of rows, or alternatively, columns, in a sequentialfashion to produce the image frame. The frames can be refreshed and/orupdated with new image data by continually repeating this process atsome desired number of frames per second.

The combination of segment and common signals applied across each pixel(that is, the potential difference across each pixel) determines theresulting state of each pixel. FIG. 4 shows an example of a tableillustrating various states of an interferometric modulator when variouscommon and segment voltages are applied. As will be readily understoodby one having ordinary skill in the art, the “segment” voltages can beapplied to either the column electrodes or the row electrodes, and the“common” voltages can be applied to the other of the column electrodesor the row electrodes.

As illustrated in FIG. 4 (as well as in the timing diagram shown in FIG.5B), when a release voltage VC_(REL) is applied along a common line, allinterferometric modulator elements along the common line will be placedin a relaxed state, alternatively referred to as a released orunactuated state, regardless of the voltage applied along the segmentlines, i.e., high segment voltage VS_(H) and low segment voltage VS_(L).In particular, when the release voltage VC_(REL) is applied along acommon line, the potential voltage across the modulator (alternativelyreferred to as a pixel voltage) is within the relaxation window (seeFIG. 3, also referred to as a release window) both when the high segmentvoltage VS_(H) and the low segment voltage VS_(L) are applied along thecorresponding segment line for that pixel.

When a hold voltage is applied on a common line, such as a high holdvoltage VC_(HOLD) _(—) _(H) or a low hold voltage VC_(HOLD) _(—) _(L),the state of the interferometric modulator will remain constant. Forexample, a relaxed IMOD will remain in a relaxed position, and anactuated IMOD will remain in an actuated position. The hold voltages canbe selected such that the pixel voltage will remain within a stabilitywindow both when the high segment voltage VS_(H) and the low segmentvoltage VS_(L) are applied along the corresponding segment line. Thus,the segment voltage swing, i.e., the difference between the high VS_(H)and low segment voltage VS_(L), is less than the width of either thepositive or the negative stability window.

When an addressing, or actuation, voltage is applied on a common line,such as a high addressing voltage VC_(ADD) _(—) _(H) or a low addressingvoltage VC_(ADD) _(—) _(L), data can be selectively written to themodulators along that line by application of segment voltages along therespective segment lines. The segment voltages may be selected such thatactuation is dependent upon the segment voltage applied. When anaddressing voltage is applied along a common line, application of onesegment voltage will result in a pixel voltage within a stabilitywindow, causing the pixel to remain unactuated. In contrast, applicationof the other segment voltage will result in a pixel voltage beyond thestability window, resulting in actuation of the pixel. The particularsegment voltage which causes actuation can vary depending upon whichaddressing voltage is used. In some implementations, when the highaddressing voltage VC_(ADD) _(—) _(H) is applied along the common line,application of the high segment voltage VS_(H) can cause a modulator toremain in its current position, while application of the low segmentvoltage VS_(L) can cause actuation of the modulator. As a corollary, theeffect of the segment voltages can be the opposite when a low addressingvoltage VC_(ADD L) is applied, with high segment voltage VS_(H) causingactuation of the modulator, and low segment voltage VS_(L) having noeffect (i.e., remaining stable) on the state of the modulator.

In some implementations, hold voltages, address voltages, and segmentvoltages may be used which always produce the same polarity potentialdifference across the modulators. In some other implementations, signalscan be used which alternate the polarity of the potential difference ofthe modulators. Alternation of the polarity across the modulators (thatis, alternation of the polarity of write procedures) may reduce orinhibit charge accumulation which could occur after repeated writeoperations of a single polarity.

FIG. 5A shows an example of a diagram illustrating a frame of displaydata in the 3×3 interferometric modulator display of FIG. 2. FIG. 5Bshows an example of a timing diagram for common and segment signals thatmay be used to write the frame of display data illustrated in FIG. 5A.The signals can be applied to the, e.g., 3×3 array of FIG. 2, which willultimately result in the line time 60 e display arrangement illustratedin FIG. 5A. The actuated modulators in FIG. 5A are in a dark-state,i.e., where a substantial portion of the reflected light is outside ofthe visible spectrum so as to result in a dark appearance to, e.g., aviewer. Prior to writing the frame illustrated in FIG. 5A, the pixelscan be in any state, but the write procedure illustrated in the timingdiagram of FIG. 5B presumes that each modulator has been released andresides in an unactuated state before the first line time 60 a.

During the first line time 60 a: a release voltage 70 is applied oncommon line 1; the voltage applied on common line 2 begins at a highhold voltage 72 and moves to a release voltage 70; and a low holdvoltage 76 is applied along common line 3. Thus, the modulators (common1, segment 1), (1,2) and (1,3) along common line 1 remain in a relaxed,or unactuated, state for the duration of the first line time 60 a, themodulators (2,1), (2,2) and (2,3) along common line 2 will move to arelaxed state, and the modulators (3,1), (3,2) and (3,3) along commonline 3 will remain in their previous state. With reference to FIG. 4,the segment voltages applied along segment lines 1, 2 and 3 will have noeffect on the state of the interferometric modulators, as none of commonlines 1, 2 or 3 are being exposed to voltage levels causing actuationduring line time 60 a (i.e., VC_(REL)—relax and VC_(HOLD) _(—)_(L)—stable).

During the second line time 60 b, the voltage on common line 1 moves toa high hold voltage 72, and all modulators along common line 1 remain ina relaxed state regardless of the segment voltage applied because noaddressing, or actuation, voltage was applied on the common line 1. Themodulators along common line 2 remain in a relaxed state due to theapplication of the release voltage 70, and the modulators (3,1), (3,2)and (3,3) along common line 3 will relax when the voltage along commonline 3 moves to a release voltage 70.

During the third line time 60 c, common line 1 is addressed by applyinga high address voltage 74 on common line 1. Because a low segmentvoltage 64 is applied along segment lines 1 and 2 during the applicationof this address voltage, the pixel voltage across modulators (1,1) and(1,2) is greater than the high end of the positive stability window(i.e., the voltage differential exceeded a predefined threshold) of themodulators, and the modulators (1,1) and (1,2) are actuated. Conversely,because a high segment voltage 62 is applied along segment line 3, thepixel voltage across modulator (1,3) is less than that of modulators(1,1) and (1,2), and remains within the positive stability window of themodulator; modulator (1,3) thus remains relaxed. Also during line time60 c, the voltage along common line 2 decreases to a low hold voltage76, and the voltage along common line 3 remains at a release voltage 70,leaving the modulators along common lines 2 and 3 in a relaxed position.

During the fourth line time 60 d, the voltage on common line 1 returnsto a high hold voltage 72, leaving the modulators along common line 1 intheir respective addressed states. The voltage on common line 2 isdecreased to a low address voltage 78. Because a high segment voltage 62is applied along segment line 2, the pixel voltage across modulator(2,2) is below the lower end of the negative stability window of themodulator, causing the modulator (2,2) to actuate. Conversely, because alow segment voltage 64 is applied along segment lines 1 and 3, themodulators (2,1) and (2,3) remain in a relaxed position. The voltage oncommon line 3 increases to a high hold voltage 72, leaving themodulators along common line 3 in a relaxed state. Then the voltage oncommon line 2 transitions back to low hold voltage 76.

Finally, during the fifth line time 60 e, the voltage on common line 1remains at high hold voltage 72, and the voltage on common line 2remains at low hold voltage 76, leaving the modulators along commonlines 1 and 2 in their respective addressed states. The voltage oncommon line 3 increases to a high address voltage 74 to address themodulators along common line 3. As a low segment voltage 64 is appliedon segment lines 2 and 3, the modulators (3,2) and (3,3) actuate, whilethe high segment voltage 62 applied along segment line 1 causesmodulator (3,1) to remain in a relaxed position. Thus, at the end of thefifth line time 60 e, the 3×3 pixel array is in the state shown in FIG.5A, and will remain in that state as long as the hold voltages areapplied along the common lines, regardless of variations in the segmentvoltage which may occur when modulators along other common lines (notshown) are being addressed.

In the timing diagram of FIG. 5B, a given write procedure (i.e., linetimes 60 a-60 e) can include the use of either high hold and addressvoltages, or low hold and address voltages. Once the write procedure hasbeen completed for a given common line (and the common voltage is set tothe hold voltage having the same polarity as the actuation voltage), thepixel voltage remains within a given stability window, and does not passthrough the relaxation window until a release voltage is applied on thatcommon line. Furthermore, as each modulator is released as part of thewrite procedure prior to addressing the modulator, the actuation time ofa modulator, rather than the release time, may determine the necessaryline time. Specifically, in implementations in which the release time ofa modulator is greater than the actuation time, the release voltage maybe applied for longer than a single line time, as depicted in FIG. 5B.In some other implementations, voltages applied along common lines orsegment lines may vary to account for variations in the actuation andrelease voltages of different modulators, such as modulators ofdifferent colors.

The details of the structure of interferometric modulators that operatein accordance with the principles set forth above may vary widely. Forexample, FIGS. 6A-6E show examples of cross-sections of varyingimplementations of interferometric modulators, including the movablereflective layer 14 and its supporting structures. FIG. 6A shows anexample of a partial cross-section of the interferometric modulatordisplay of FIG. 1, where a strip of metal material, i.e., the movablereflective layer 14 is deposited on supports 18 extending orthogonallyfrom the substrate 20. In FIG. 6B, the movable reflective layer 14 ofeach IMOD is generally square or rectangular in shape and attached tosupports at or near the corners, on tethers 32. In FIG. 6C, the movablereflective layer 14 is generally square or rectangular in shape andsuspended from a deformable layer 34, which may include a flexiblemetal. The deformable layer 34 can connect, directly or indirectly, tothe substrate 20 around the perimeter of the movable reflective layer14. These connections are herein referred to as support posts. Theimplementation shown in FIG. 6C has additional benefits deriving fromthe decoupling of the optical functions of the movable reflective layer14 from its mechanical functions, which are carried out by thedeformable layer 34. This decoupling allows the structural design andmaterials used for the reflective layer 14 and those used for thedeformable layer 34 to be optimized independently of one another.

FIG. 6D shows another example of an IMOD, where the movable reflectivelayer 14 includes a reflective sub-layer 14 a. The movable reflectivelayer 14 rests on a support structure, such as support posts 18. Thesupport posts 18 provide separation of the movable reflective layer 14from the lower stationary electrode (i.e., part of the optical stack 16in the illustrated IMOD) so that a gap 19 is formed between the movablereflective layer 14 and the optical stack 16, for example when themovable reflective layer 14 is in a relaxed position. The movablereflective layer 14 also can include a conductive layer 14 c, which maybe configured to serve as an electrode, and a support layer 14 b. Inthis example, the conductive layer 14 c is disposed on one side of thesupport layer 14 b, distal from the substrate 20, and the reflectivesub-layer 14 a is disposed on the other side of the support layer 14 b,proximal to the substrate 20. In some implementations, the reflectivesub-layer 14 a can be conductive and can be disposed between the supportlayer 14 b and the optical stack 16. The support layer 14 b can includeone or more layers of a dielectric material, for example, siliconoxynitride (SiON) or silicon dioxide (SiO₂). In some implementations,the support layer 14 b can be a stack of layers, such as, for example, aSiO₂/SiON/SiO₂ tri-layer stack. Either or both of the reflectivesub-layer 14 a and the conductive layer 14 c can include, e.g., analuminum (Al) alloy with about 0.5% copper (Cu), or another reflectivemetallic material. Employing conductive layers 14 a, 14 c above andbelow the dielectric support layer 14 b can balance stresses and provideenhanced conduction. In some implementations, the reflective sub-layer14 a and the conductive layer 14 c can be formed of different materialsfor a variety of design purposes, such as achieving specific stressprofiles within the movable reflective layer 14.

As illustrated in FIG. 6D, some implementations also can include a blackmask structure 23. The black mask structure 23 can be formed inoptically inactive regions (e.g., between pixels or under posts 18) toabsorb ambient or stray light. The black mask structure 23 also canimprove the optical properties of a display device by inhibiting lightfrom being reflected from or transmitted through inactive portions ofthe display, thereby increasing the contrast ratio. Additionally, theblack mask structure 23 can be conductive and be configured to functionas an electrical bussing layer. In some implementations, the rowelectrodes can be connected to the black mask structure 23 to reduce theresistance of the connected row electrode. The black mask structure 23can be formed using a variety of methods, including deposition andpatterning techniques. The black mask structure 23 can include one ormore layers. For example, in some implementations, the black maskstructure 23 includes a molybdenum-chromium (MoCr) layer that serves asan optical absorber, a SiO₂ layer, and an aluminum alloy that serves asa reflector and a bussing layer, with a thickness in the range of about30-80 Å, 500-1000 Å, and 500-6000 Å, respectively. The one or morelayers can be patterned using a variety of techniques, includingphotolithography and dry etching, including, for example, carbontetrafluoromethane (CF₄) and/or oxygen (O₂) for the MoCr and SiO₂ layersand chlorine (Cl₂) and/or boron trichloride (BCl₃) for the aluminumalloy layer. In some implementations, the black mask 23 can be an etalonor interferometric stack structure. In such interferometric stack blackmask structures 23, the conductive absorbers can be used to transmit orbus signals between lower, stationary electrodes in the optical stack 16of each row or column. In some implementations, a spacer layer 35 canserve to generally electrically isolate the absorber layer 16 a from theconductive layers in the black mask 23.

FIG. 6E shows another example of an IMOD, where the movable reflectivelayer 14 is self-supporting. In contrast with FIG. 6D, theimplementation of FIG. 6E does not include support posts 18. Instead,the movable reflective layer 14 contacts the underlying optical stack 16at multiple locations, and the curvature of the movable reflective layer14 provides sufficient support that the movable reflective layer 14returns to the unactuated position of FIG. 6E when the voltage acrossthe interferometric modulator is insufficient to cause actuation. Theoptical stack 16, which may contain a plurality of several differentlayers, is shown here for clarity including an optical absorber 16 a,and a dielectric 16 b. In some implementations, the optical absorber 16a may serve both as a fixed electrode and as a partially reflectivelayer.

In implementations such as those shown in FIGS. 6A-6E, the IMODsfunction as direct-view devices, in which images are viewed from thefront side of the transparent substrate 20, i.e., the side opposite tothat upon which the modulator is arranged. In these implementations, theback portions of the device (that is, any portion of the display devicebehind the movable reflective layer 14, including, for example, thedeformable layer 34 illustrated in FIG. 6C) can be configured andoperated upon without impacting or negatively affecting the imagequality of the display device, because the reflective layer 14 opticallyshields those portions of the device. For example, in someimplementations a bus structure (not illustrated) can be included behindthe movable reflective layer 14 which provides the ability to separatethe optical properties of the modulator from the electromechanicalproperties of the modulator, such as voltage addressing and themovements that result from such addressing. Additionally, theimplementations of FIGS. 6A-6E can simplify processing, such aspatterning.

FIG. 7 shows an example of a flow diagram illustrating a manufacturingprocess 80 for an interferometric modulator, and FIGS. 8A-8E showexamples of cross-sectional schematic illustrations of correspondingstages of such a manufacturing process 80. In some implementations, themanufacturing process 80 can be implemented to manufacture, e.g.,interferometric modulators of the general type illustrated in FIGS. 1and 6, in addition to other blocks not shown in FIG. 7. With referenceto FIGS. 1, 6 and 7, the process 80 begins at block 82 with theformation of the optical stack 16 over the substrate 20. FIG. 8Aillustrates such an optical stack 16 formed over the substrate 20. Thesubstrate 20 may be a transparent substrate such as glass or plastic, itmay be flexible or relatively stiff and unbending, and may have beensubjected to prior preparation processes, e.g., cleaning, to facilitateefficient formation of the optical stack 16. As discussed above, theoptical stack 16 can be electrically conductive, partially transparentand partially reflective and may be fabricated, for example, bydepositing one or more layers having the desired properties onto thetransparent substrate 20. In FIG. 8A, the optical stack 16 includes amultilayer structure having sub-layers 16 a and 16 b, although more orfewer sub-layers may be included in some other implementations. In someimplementations, one of the sub-layers 16 a, 16 b can be configured withboth optically absorptive and conductive properties, such as thecombined conductor/absorber sub-layer 16 a. Additionally, one or more ofthe sub-layers 16 a, 16 b can be patterned into parallel strips, and mayform row electrodes in a display device. Such patterning can beperformed by a masking and etching process or another suitable processknown in the art. In some implementations, one of the sub-layers 16 a,16 b can be an insulating or dielectric layer, such as sub-layer 16 bthat is deposited over one or more metal layers (e.g., one or morereflective and/or conductive layers). In addition, the optical stack 16can be patterned into individual and parallel strips that form the rowsof the display.

The process 80 continues at block 84 with the formation of a sacrificiallayer 25 over the optical stack 16. The sacrificial layer 25 is laterremoved (e.g., at block 90) to form the cavity 19 and thus thesacrificial layer 25 is not shown in the resulting interferometricmodulators 12 illustrated in FIG. 1. FIG. 8B illustrates a partiallyfabricated device including a sacrificial layer 25 formed over theoptical stack 16. The formation of the sacrificial layer 25 over theoptical stack 16 may include deposition of a xenon difluoride(XeF₂)-etchable material such as molybdenum (Mo) or amorphous silicon(Si), in a thickness selected to provide, after subsequent removal, agap or cavity 19 (see also FIGS. 1 and 8E) having a desired design size.Deposition of the sacrificial material may be carried out usingdeposition techniques such as physical vapor deposition (PVD, e.g.,sputtering), plasma-enhanced chemical vapor deposition (PECVD), thermalchemical vapor deposition (thermal CVD), or spin-coating.

The process 80 continues at block 86 with the formation of a supportstructure e.g., a post 18 as illustrated in FIGS. 1, 6 and 8C. Theformation of the post 18 may include patterning the sacrificial layer 25to form a support structure aperture, then depositing a material (e.g.,a polymer or an inorganic material, e.g., silicon oxide) into theaperture to form the post 18, using a deposition method such as PVD,PECVD, thermal CVD, or spin-coating. In some implementations, thesupport structure aperture formed in the sacrificial layer can extendthrough both the sacrificial layer 25 and the optical stack 16 to theunderlying substrate 20, so that the lower end of the post 18 contactsthe substrate 20 as illustrated in FIG. 6A. Alternatively, as depictedin FIG. 8C, the aperture formed in the sacrificial layer 25 can extendthrough the sacrificial layer 25, but not through the optical stack 16.For example, FIG. 8E illustrates the lower ends of the support posts 18in contact with an upper surface of the optical stack 16. The post 18,or other support structures, may be formed by depositing a layer ofsupport structure material over the sacrificial layer 25 and patterningportions of the support structure material located away from aperturesin the sacrificial layer 25. The support structures may be locatedwithin the apertures, as illustrated in FIG. 8C, but also can, at leastpartially, extend over a portion of the sacrificial layer 25. As notedabove, the patterning of the sacrificial layer 25 and/or the supportposts 18 can be performed by a patterning and etching process, but alsomay be performed by alternative etching methods.

The process 80 continues at block 88 with the formation of a movablereflective layer or membrane such as the movable reflective layer 14illustrated in FIGS. 1, 6 and 8D. The movable reflective layer 14 may beformed by employing one or more deposition steps, e.g., reflective layer(e.g., aluminum, aluminum alloy) deposition, along with one or morepatterning, masking, and/or etching steps. The movable reflective layer14 can be electrically conductive, and referred to as an electricallyconductive layer. In some implementations, the movable reflective layer14 may include a plurality of sub-layers 14 a, 14 b, 14 c as shown inFIG. 8D. In some implementations, one or more of the sub-layers, such assub-layers 14 a, 14 c, may include highly reflective sub-layers selectedfor their optical properties, and another sub-layer 14 b may include amechanical sub-layer selected for its mechanical properties. Since thesacrificial layer 25 is still present in the partially fabricatedinterferometric modulator formed at block 88, the movable reflectivelayer 14 is typically not movable at this stage. A partially fabricatedIMOD that contains a sacrificial layer 25 also may be referred to hereinas an “unreleased” IMOD. As described above in connection with FIG. 1,the movable reflective layer 14 can be patterned into individual andparallel strips that form the columns of the display.

The process 80 continues at block 90 with the formation of a cavity,e.g., cavity 19 as illustrated in FIGS. 1, 6 and 8E. The cavity 19 maybe formed by exposing the sacrificial material 25 (deposited at block84) to an etchant. For example, an etchable sacrificial material such asMo or amorphous Si may be removed by dry chemical etching, e.g., byexposing the sacrificial layer 25 to a gaseous or vaporous etchant, suchas vapors derived from solid XeF₂ for a period of time that is effectiveto remove the desired amount of material, typically selectively removedrelative to the structures surrounding the cavity 19. Other etchingmethods, e.g. wet etching and/or plasma etching, also may be used. Sincethe sacrificial layer 25 is removed during block 90, the movablereflective layer 14 is typically movable after this stage. After removalof the sacrificial material 25, the resulting fully or partiallyfabricated IMOD may be referred to herein as a “released” IMOD.

In some implementations described herein, at least part of a combinedsensor device may be incorporated in a cover glass apparatus that can beoverlaid on or otherwise combined with a display. The cover glassapparatus may have 2, 3 or more layers. In some implementations, thecover glass apparatus may include a substantially transparent andflexible upper substrate and a substantially transparent and relativelymore rigid lower substrate. The cover glass may include intermediatelayers disposed on and/or between the substrates, such as electrodes, asubstantially transparent elastomeric layer and/or force-sensitiveresistor material. In some such implementations, the lower substrate ofthe cover glass apparatus may be overlaid on a display substrate.

FIG. 9A shows an example of sensor electrodes formed on substrates of acover glass apparatus. In the example shown in FIG. 9A, three rows 915of diamond-shaped substantially transparent electrodes are depicted onthe substantially transparent upper substrate 905 and seven columns 920of substantially transparent diamond-shaped electrodes are located onthe substantially transparent lower substrate 910. Relatively few rowsand columns are shown here for illustrative purposes, while in actualsensor devices the number of rows and columns may extend from tens tohundreds or even a thousand or more. One may note that the rows andcolumns are largely interchangeable, and no limitation is intended here.In some implementations, the upper substrate 905 of the combined sensordevice 900 may be formed of a relatively flexible material, such as aflexible polymer. In some such examples, the upper substrate 905 may bea clear plastic film made of polyethylene terephthalate (PET),polyethylene naphthalate (PEN), polyimide, or a similar material. Insome implementations, the upper substrate 905 may have a modulus ofelasticity in the range of 0.5-5 GPa. The lower substrate 910 may beformed of glass, plastic, a polymer, etc. In some implementations, thelower substrate 910 may be a display substrate. For example, in someimplementations the lower substrate 910 may be the same substrate as thetransparent substrate 20 described above.

In this example, every other column electrode 920 includes diamondelectrodes that are located directly under corresponding diamonds of therow electrodes 915 in overlapping regions 925 a. Some implementationshave offsets of the diamonds of the row electrodes 915 and the columnelectrodes 920, whereby the diamonds in the row electrodes 915 and thecolumns 920 partially overlie each other.

In some implementations, the row electrodes 915 and/or the columnelectrodes 920 may be formed into other shapes, such as squares,rectangles, triangles, circles, ovals, etc., and shapes that includepredominantly open regions in the center of the shape such as a frame, aring, or a series of connected line segments. A description of some suchshapes is included in various parts of pending U.S. patent applicationSer. No. 12/957,025 filed Dec. 21, 2010 and entitled “Capacitive TouchSensing Devices and Methods of Manufacturing Thereof,” (see, e.g., FIGS.11A-11J and the corresponding description) the contents of which arehereby incorporated by reference in their entirety. Moreover, inalternative implementations the row electrodes 915 may be formed on thelower substrate 910 and the column electrodes 920 may be formed on theupper substrate 905. In some implementations, such as that describedbelow with reference to FIGS. 10C and 10D including a compressiblematerial 1025 positioned between the row electrodes 915 and the columnelectrodes 920, a light touch may be detected by measuring the change inmutual capacitance between adjacent diamonds (also referred to asprojective capacitive touch (PCT)). In such implementations, contactwith a stylus may be detected when the upper substrate 905 is depressedby measuring the change in capacitance between the row electrodes 915and the column electrodes 920.

In implementations with a patterned dielectric material between the rowelectrodes 915 and the column electrodes 920, gaps may be formed betweencorresponding row electrodes 915 and column electrodes 920. In suchimplementations, light touches can be detected with PCT measurementsbetween adjacent electrodes, and stylus depressions can be detectedeither by a change in the effective parallel plate capacitance betweenthe row electrodes 915 and the column electrodes 920 (see FIG. 10B) orby measuring changes in resistance that occur when the row electrodes915 and the column electrodes 920 come in direct mechanical andelectrical contact (see FIG. 10A), or by measuring changes in aforce-sensitive resistor positioned between row electrodes 915 andcolumn electrodes 920 when pressed with a finger, a stylus tip, ridgesof a finger, or the like (see FIG. 10D). The force-sensitive resistorsmay be included between row electrodes 915 and column electrodes 920 ina handwriting and touch sensor zone 1005, in a fingerprint sensor zone1010, or both. In some such implementations, a high resistivity layermay be formed on the row electrodes 915 or the column electrodes 920 tominimize the effect of parasitic signals during the sensing of thelocation of the stylus.

FIG. 9B shows an alternative example of sensor electrodes formed on acover glass. In the example shown in FIG. 9B, the column electrodes 920in which diamonds lay beneath the diamonds of the row electrodes 915have been removed from the design. Ohmic membrane switches, resistivemembrane switches, resistive switches with force-sensitive resistive(FSR) material, FSR switches with a fixed series resistor, or capacitivemembranes of the combined sensor device 900 may be formed at theintersections between the row electrodes 915 and the column electrodes920 (in overlapping regions 925 b) for detecting stylus contact and, insome cases, a fingertip or ridges of a finger. Such implementations canreduce the number of column electrodes 920 (note that the number ofcolumn electrodes 920 and associated connection pads in FIG. 9B is fewerthan the column electrodes 920 and connection pads in FIG. 9A) that needto be connected to the external processing circuitry, because the samecolumns can serve the purpose of detecting a light touch through the PCTmethod or detecting the stylus contact through either a capacitancechange method or a resistive change method.

For example, in the touch mode, only a very light force may be requiredto register a touch. However, in the handwriting mode, the sensor may beconfigured to accept many forms of stylus, pen, or other pointer input,regardless of whether or not the pointing device is conducting ornon-conducting. Some implementations described herein provide sensorscapable of distinguishing a large number of multi-touch eventssimultaneously, such as may occur when reading a fingerprint whileoperating in a fingerprint sensor mode, or detecting and rejecting aninadvertent palm touch when operating in a handwriting sensor mode.

FIG. 10A shows an example of a cross-sectional view of a combined sensordevice. While the sensor array shown in FIG. 10A is depicted as acombination touch, stylus, and fingerprint sensor, it should be notedthat the configuration of FIG. 10A and other configurations describedbelow may serve as only a touch sensor, a stylus sensor, a fingerprintsensor, or a combination thereof. In the example shown in FIG. 10A, tworepeating cells are shown in a first region referred to as a handwritingand touch sensor zone 1005. Such sensing elements may be referred toherein as “sensels.” An optional second region, referred to as afingerprint sensor zone 1010, generally has a finer pitch betweenelectrodes to allow for higher resolution often needed for fingerprintdetection. As noted elsewhere herein, in some implementations thefingerprint sensor and the handwriting and touch sensor are not indifferent zones. FIGS. 10B-10D show examples of cross-sectional views ofalternative combined sensor devices. FIGS. 10A-10D, like many otherdrawings provided herein, may not be drawn to scale. Touch, handwriting,and fingerprint zones are shown in FIGS. 10A-10D, although not all zoneswould normally be activated simultaneously. Nor may all zones andoperating modes be available in a sensor device. Single ormulti-touching using one or more fingers is depicted as being sensedusing PCT in handwriting and touch sensor zone 1005, where particularlylight touches as well as moderate and heavy touches may be detected. Inthe example shown in FIG. 10A, proximity of a finger 1047 alters theelectric field 1050 between the upper electrode 1015 and the lowerelectrode 1030 b, producing a change in mutual capacitance. This effectis schematically depicted by the variable capacitor of the associatedcircuit diagram 1055 a. In some implementations, the upper electrode1015 may be a row electrode and, as mentioned above, in some otherimplementations the upper electrode 1015 may be a column electrode (seeFIGS. 9A and 9B).

High forces or high localized pressure (such as that incurred when a tipof a stylus such as a pen, pencil, or pointer is pressed against thesurface of the combined sensor device 900) may be detected with ohmic orresistive membrane switches. One example is shown in FIG. 10A, in whichhigh localized pressure produced by a pen or stylus 1042 can be detectedby a mechanical switch that includes the upper electrode 1015 and thelower electrode 1030 a. A resistor 1035, sometimes referred to as afixed resistor, may be positioned between upper electrode 1015 and lowerelectrode 1030 a to prevent direct shorting of the upper electrode 1015and the lower electrode 1030 a. The switch including a vertical orserpentine fixed resistor is represented schematically in the circuitdiagram 1055 a. The resistor 1035 may have an additional metal layerdisposed thereon (not shown) to aid in electrical contact between it andthe upper electrode 1015. While a resistive membrane switch as definedhere includes at least a fixed resistor in each sensel (the resistivemembrane switch also may include a force-sensitive resistor in serieswith the fixed resistor or in lieu of the fixed resistor), an ohmicmembrane switch does not require an additional fixed resistor in serieswith the upper and lower electrodes. The fixed resistor may be formed ofan ohmic material in some implementations. In some otherimplementations, the fixed resistor may be a non-linear device such as aleaky diode or other device that provides a relatively high resistanceto current flow. The fixed resistor may include a thin-film conductivecap that serves as a conductive contact surface. Whereas a one-to-onecorrespondence with digital resistive touch (DRT) lower electrodes 1030a and PCT lower electrodes 1030 b is shown in FIG. 10A, in someconfigurations the PCT lower electrodes 1030 b could span one or moreadjacent sensels. In some configurations, the PCT lower electrode 1030 bis wider and longer than the DRT lower electrode 1030 a.

In some implementations, the upper electrodes 1015 and the lowerelectrodes 1030 a may be configured to form two plates of a deformableparallel plate capacitor, instead of the mechanical switch describedabove. In some implementations, the electrodes 1015 and 1030 a may beseparated by an air gap, as shown in areas 1065 of FIG. 10B, and mayhave a spacing corresponding to a baseline capacitance in the normalunpressed state. Upon the application of force or pressure, upperelectrode 1015 is displaced and the electrodes 1015 and 1030 a comecloser. When the inter-electrode distance between the electrodes 1015and 1030 a is reduced, the capacitance changes (e.g., increases),enabling the sensing of an analog change in the displacement andallowing inference of the presence of the applied force or pressure.Accordingly, high localized pressure or force from a pen, a stylus,etc., may be detected via parallel plate capacitance changes betweenupper electrodes 1015 and lower electrodes 1030 a. The capacitancechanges caused by such localized changes in pressure are representedschematically by the variable capacitor 1056 of the circuit diagram 1055b. In the configuration shown, the fixed resistor 1035 is in series withthe variable capacitor 1056. In other configurations (not shown), thefixed resistor 1035 may be omitted.

In some implementations, an interlayer separation 1032 may be formedbetween the upper substrate 905 and the lower substrate 910 by disposinga compressible layer 1025 between the upper and lower electrodes. Insome implementations, the compressible layer 1025 may be a patternable,thin (e.g., 1 to 10 microns) polymer with a low elastic modulus, such asan elastomer. In some such implementations, the compressible layer 1025may allow direct measurement of capacitance changes when the uppersubstrate 905 is depressed by a touch of a pen, a stylus, a finger, etc.and the distance between an upper electrode 1015 and a lower electrode1030 a changes. The compressible layer 1025 may have a lower modulus ofelasticity than the upper substrate 905. For example, the uppersubstrate 905 may be a clear plastic film made of PET, PEN, polyimide,or a similar material having a modulus of elasticity in the range of0.5-5 GPa. The compressible layer 1025 may have a significantly lowermodulus of elasticity, such as in the range of 0.5-50 MPa.

In some implementations, the compressible layer 1025 may be patterned toinclude spaces or voids (which also may be referred to herein as “airgaps”) between the upper substrate 905 and the lower substrate 910. Someimplementations, such as those shown in FIGS. 10A and 10B, include voidsin the areas 1065, wherein the compressible layer 1025 is not formedbetween the upper electrodes 1015 and the lower electrodes 1030 a.However, in these examples the compressible layer 1025 extends withoutvoids between the upper substrate 905 and the lower electrodes 1030 b inthe areas 1070. According to some such implementations, the compressiblelayer 1025 may be patterned such that there are air gaps in the areas1065 and 1080. The indicated thickness and spacing of the compressiblelayer 1025 regions are merely indicated by way of example. The locationsand lateral dimensions of the air gaps in the areas 1065 and 1080 may beselected according to desired parameters of force sensitivity,reliability and/or optical performance, as a person having ordinaryskill in the art will readily comprehend. For example, the interlayerseparation 1032 may be a fraction of a micron to several microns. Thethickness of the air gaps in the areas 1065 and 1080 also may be afraction of a micron to several microns thick. The pitch or spacingbetween adjacent upper electrodes 1015 (adjacent sensels) may range froma few tenths of a millimeter to over five millimeters in the handwritingand touch sensor zone 1005 (with the pitch between lower electrodes 1030a and 1030 b approximately half that), while the pitch or spacingbetween adjacent electrodes 1040 in the fingerprint sensor zone 1010 maybe as small as 50 microns or so.

The compressible layer 1025 may aid in enabling measurable deflectionsof the upper substrate 905. In some implementations, the compressiblelayer 1025 also may be formed in the areas 1065, as shown in FIG. 10Cand described below. In some such implementations, the compressiblelayer 1025 may include an elastomeric material (or a similar material)that allows direct measurement of capacitance changes when the uppersubstrate 905 is depressed by a touch of a pen, a stylus, a finger, etc.and the distance between an upper electrode 1015 and a lower electrode1030 a changes. Alternatively the mutual capacitance between an upperelectrode 1015 and a laterally displaced lower electrode 1030 b also maychange to allow the detection of a pen, stylus, finger, etc.

The fingerprint sensor zone 1010 may be configured for fingerprintdetection. In the implementation shown in FIG. 10A, the upperfingerprint electrodes 1020 and the lower fingerprint electrodes 1040form an array of resistive membrane switches, one of which isschematically represented in the circuit diagram 1060 a. In the examplesshown in FIGS. 10A-10C, the compressible layer 1025 is not formedbetween the upper fingerprint electrodes 1020 and the lower fingerprintelectrodes 1040 in the area 1080. However, in the implementationdepicted in FIG. 10D (which will be described in more detail below), thecompressible layer 1025 is formed in the area 1080 except for regionswhere FSR material 1085 is located.

In the examples shown in FIGS. 10A-10D, the upper fingerprint electrodes1020 and the lower fingerprint electrodes 1040 have a smaller pitch thanthat of the upper electrodes 1015 and the lower electrodes 1030 in thehandwriting and touch sensor zone 1005, in order to provide relativelyhigher resolution in the fingerprint sensor zone 1010. However, in somealternative implementations, the pitch of the upper fingerprintelectrodes 1020 and the lower fingerprint electrodes 1040 may besubstantially the same as that of the upper electrodes 1015 and thelower electrodes 1030 in the handwriting and touch sensor zone 1005.

The compressible layer 1025 may be patterned using lithography and etchtechniques (or other lithography-based techniques). In someimplementations, the compressible layer 1025 can keep the ohmic orresistive switches of areas 1065 and 1080 open until a suitable force isapplied to the outer surface of the sensor (which is the top surface ofthe upper substrate 905 in this example). Because the compressible layer1025 is part of a sensor that would overlay a display, the compressiblelayer 1025 can be substantially transparent.

In some implementations, the compressible layer 1025 may have an indexof refraction closely matched to that of the lower substrate 910 and theupper substrate 905. In some implementations, the compressible layer1025 may have an index of refraction that differs from that of the lowersubstrate 910 and the upper substrate 905 by less than 5%, by less than10%, by less than 20%, etc. For example, a 6% or less difference in theindex of refraction may result in less than 0.2% reduction intransmission through the material stack. Such implementations canprovide good optical transmission in areas where the compressible layer1025 extends from the upper substrate 905 to the lower substrate 910.However, the optical transmission may be reduced in the air gap regions,caused by reflections at each air-material interface. Such reflectionsmay be greater than, e.g., 4%, as calculated using the index ofrefraction of the upper substrate 905 (which may be approximatelyn=˜1.5) and the index of refraction of air (n_(o)=1), in Equation 1:

(n−n _(o))²/(n+n _(o))² =R, where R is reflectance.  (Equation 1)

Accordingly, implementations having air gaps with minimal lateraldimensions can provide better optical performance. However, some suchimplementations may result in less deflection for a given pressure andmay therefore be less sensitive to pressure or applied forces.

Therefore, some implementations provide an index-matched compressiblelayer 1025, which can improve the optical performance. Even in someimplementations having air gaps in the areas 1065, the opticalperformance may already be quite good due to an architecture having theareas 1065 occupy a relatively small fraction of the handwriting andtouch sensor zone 1005. For example, the areas 1065 with air gaps mayoccupy less than about 50% of the total area, whereas in other examplesthe areas 1065 may occupy less than about 10% of the total area. In suchimplementations, the majority of the sensor area will not have an airgap, and therefore will exhibit much reduced reflection at the layer905/layer 1025 and the layer 1025/layer 910 interfaces, i.e., such thatthe total reflection for both interfaces may be <<1%, as estimated perEquation 1.

The sensitivity to pressure or force from a pen, stylus, or finger ofthe individual sensing elements (regardless of whether they are used ina resistive switch mode or in a deformable parallel plate capacitormode) may be increased by the use of a low-modulus compressible layer1025, as shown in FIGS. 11A-11D. The low-modulus compressible layer 1025may remove the clamped boundary condition that can be imposed by ahigher-modulus material. Having a low modulus compressible layer 1025can effectively increase the diameter of an area 1110 of thecompressible layer 1025 that is deflected by the stylus tip 1105,thereby increasing the deflection of the upper substrate 905 in the area1110.

FIGS. 11A-11D show examples of cross-sectional views of combined sensordevices having high-modulus and low-modulus compressible layers. FIG.11A shows a stylus tip 1105 in contact with a flexible upper substrate905 of a portion of a simplified combination touch, handwriting, andfingerprint sensor, wherein the compressible layer 1025 a is a patternedhigh-modulus material that is sandwiched between the upper substrate 905and the lower substrate 910. Air gaps 1115 in the compressible layer1025 a allow the upper substrate 905 of the combined sensor device 900to deform with applied forces, although the deflected area 1110 obtainedis limited in part by the small air gaps 1115 in the relatively stiffcompressible layer 1025 a.

FIG. 11B shows a low-modulus compressible layer 1025 b sandwichedbetween the relatively more flexible upper substrate 905 and therelatively less flexible lower substrate 910. In this example, thedeflected area 1110 of the upper substrate 905 from stylus forces islarger due to the ability of the compressible layer 1025 b to compressand deform as the stylus tip 1105 is pressed against the outer surfaceof the upper substrate 905. In the example shown in FIG. 11C, the stylus1105 has been pressed hard enough for the flexible upper substrate 905to make (or nearly make) physical contact with the lower substrate 910.

Use of a low-modulus elastomeric compressible layer 1025 b also mayeffectively increase the lateral resolution from applied pressure orforce without decreasing the pitch of the row or column electrodes, asillustrated in FIG. 11D. Appreciable deflections of the upper substrate905 can occur even when the tip of the stylus tip 1105 is not directlyabove an air gap 1115 in the compressible layer 1025, thus allowingdetection of the stylus tip 1105 even if the combined sensor device 900has relatively wide spacings between adjacent sensing elements. Forexample, handwriting might be resolved at a resolution of 0.2 mm even ifthe pitch between adjacent rows or columns were 0.5 mm by averaging theresponses from adjacent sensels. By allowing a relatively larger pitchbetween adjacent rows or columns, such configurations may enable thereduction of the total number of row electrodes and column electrodesfor a given resolution, thereby reducing the number of I/Os on thehandwriting sensor controller. This reduction can reduce the number ofleadouts and reduce the cost and complexity of the handwritingcontroller.

An alternative implementation of a combination sensor is shown in FIG.10C. As compared to the implementations shown in FIGS. 10A and 10B, theair gaps have been removed from the areas 1065 of the handwriting andtouch sensor zone 1005. Thus, the optical performance of the handwritingand touch sensor zone 1005 may be enhanced with respect to theimplementation of the combined sensor device 900 shown in FIGS. 10A and10B. The handwriting sensor in the implementation of the combined sensordevice 900 shown in FIG. 10C functions as a variable parallel platecapacitor, where heavy touches or deflections of the upper layer aredetected from changes in the parallel plate capacitance. Thisfunctionality is represented by the variable capacitor 1056 of thecircuit diagram 1055 c.

FIG. 10D illustrates another example of an alternative implementation.In the example shown in FIG. 10D, the air gaps have been removed in thearea 1080 of the fingerprint sensor zone 1010 and replaced with acommercially available FSR material 1085. The FSR material 1085 providesa relatively high value of resistance when not compressed and arelatively low value of resistance when compressed, thereby functioningas a switch though without a direct contact region. This functionalityis represented by the variable resistor 1087 of the circuit diagram 1060b. A fixed resistor 1045 such as a vertical resistor or a serpentineresistor may be included in series with the FSR material 1085 in eachsensel. Transparent FSR material 1085 that includes either transparentparticles or low fill ratios of particles may be used in someimplementations. Non-transparent FSR material 1085 may be used in someapplications where, for example, the diameter or width of the resistorsis sufficiently small (on the order of a few to tens of microns) toavoid excessive occlusion of an underlying display.

FIG. 12 shows an example of a device that includes a cover glass with acombination touch, handwriting and fingerprint sensor. In this example,the cover glass includes an implementation of the combined sensor device900 and is overlaid on the display of a display device 40, such as amobile phone. Some examples of the display device 40 are described belowwith reference to FIGS. 25A and 25B. The combined sensor device 900 canserve as a single or multi-touch sensor, a handwriting input sensor, anda fingerprint image sensor. In this example, the fingerprint sensor zone1010 is in a dedicated portion above the display. The remaining portionof the combined sensor device 900 is configured as the handwriting andtouch sensor zone 1005. In some other configurations, fingerprint sensorzone 1010 may be positioned anywhere throughout the combined sensordevice 900. In yet other configurations, the position of fingerprintsensor zone 1010 is software programmable and software selectable.

An example of touch mode operation will now be described with referenceto FIG. 10A. When a finger is used to touch anywhere in the handwritingand touch sensor zone 1005, either all or a selected subset of the upperelectrodes 1015 on the upper substrate 905 and the lower electrodes 1030b on the lower substrate 910 may be addressed during a scanningsequence. In some implementations, the capacitance between the upperelectrodes 1015 and the lower electrodes 1030 b may be measured at eachof the intersections between row and column electrodes (see FIGS. 9A and9B). The conducting surface of the finger 1047 interferes with theelectric field lines 1050, as shown in FIGS. 10A-10D, and modifies thecapacitance between the upper electrodes 1015 and the lower electrodes1030 b. Detecting this change in capacitance allows a reading of whichsensels of the handwriting and touch sensor zone 1005 are in thevicinity of the finger. In this example, the electrodes on the uppersubstrate 905 and the lower substrate 910 that are scanned during touchmode are not necessarily disposed directly above and below each other.In the examples shown in FIGS. 10A-10D, a change in capacitance can bedetected between an upper electrode 1015 on the upper substrate 905 andan adjacent lower electrode 1030 b of the lower substrate 910. Note thatfor this PCT measurement, a very light touch or even the proximity of afinger may be detectable, because the capacitance change does not dependon the pressure being applied to the upper substrate 905.

When a pointing device, such as a stylus (either conducting ornon-conducting) is placed on the sensor surface, the resultant pressurecan be significantly higher than that associated with a finger touch,due to the smaller area of contact between the stylus and the surface.This pressure can be up to two orders of magnitude (or more) greaterthan the pressure exerted by a finger touch. In some implementations,during the readout process in handwriting mode, a different set ofelectrodes from those used for the touch mode (such as upper electrodes1015 and lower electrodes 1030 a depicted in FIG. 10A) may be excitedand a different circuit may be deployed for the measurement. Thedifferent circuit may sense either the closure of a switch for animplementation such as that shown in FIG. 10A, or the change in parallelplate capacitance for an implementation such as that shown in FIGS.10B-10D.

In some implementations, the addressing and/or measurement circuitry fora touch mode, handwriting mode and/or fingerprint sensing mode may becontained within one or more controller or driver Application SpecificIntegrated Circuit (ASIC) chips. The ASIC chip or chips may be attacheddirectly to the underside of the upper substrate 905 or connectedelectrically to the electrodes on the upper substrate 905 and the lowersubstrate 910 by means such as direct die attach using solder oranisotropic conductive film, or connection through a cable or traces ona flex tape that are coupled to ICs on the tape or on an externalprinted circuit board.

In some implementations described above, the electrodes scanned duringthe handwriting mode on the upper substrate 905 and the lower substrate910 are disposed directly above and below each other (for example, seeFIG. 10A). When the stylus tip 1105 (which may be a tip of pen 1042 asshown in FIG. 10A or 10B) is applied with sufficient force, the pressureexerted by the stylus tip 1105 may cause the upper substrate 905 and thecompressible layer 1025 to deflect (see FIG. 11C) and may cause theupper electrodes 1015 and the resistor 1035 on the lower electrode 1030a to make physical contact, resulting in a closure of a membrane switch(see FIG. 10A). A large resistance at each switch may be enabled by theinclusion of a fixed resistor 1035. This resistance may substantiallylower the current and allow determination of the sensel locations thatare being pressed in the handwriting, fingerprint or touch mode when oneor more membrane switches are being pressed simultaneously. This mayoccur, for example, when a palm is resting on the surface of thecombined sensor device 900 and a stylus is also applied to the surface.The resistor 1035 may be formed from a resistive layer that isfabricated to be in series with the lower electrodes 1030 a.Alternatively, the displacement of the upper substrate 905 with theforce or pressure from a stylus or finger on the outer surface can bemeasured from a change in the parallel plate capacitance between anupper electrode 1015 and a corresponding lower electrode 1030 a.

Some implementations allow operation of the combined sensor device 900in a fingerprint acquisition mode, such as in a specific region of thecombined sensor device 900 that is configured to enable this mode.Examples of fingerprint sensor zones 1010 are shown in the far rightportion of FIGS. 10A-10D and in the lower right portion of FIG. 12. Insome implementations, the fingerprint sensor zones 1010 may befabricated using the same process flow and materials as those used forfabricating the rest of the combined sensor device 900. However, in someimplementations, the fingerprint sensor zone 1010, the upper fingerprintelectrodes 1020 and the lower fingerprint electrodes 1040, as well asthe resistors 1045 of the lower fingerprint electrodes 1040, may bearranged with a significantly closer pitch or spacing than the upperelectrodes 1015 or the lower electrodes 1030 of the handwriting andtouch sensor zone 1005. For example, the pitch or spacing in thefingerprint sensor zone 1010 may be on the order of about 10 microns to100 microns. Such configurations can provide a sensor with sufficientlyhigh resolution to distinguish between the ridges and valleys of afingerprint.

When a finger is pressed down on the surface of the upper substrate 905in the fingerprint sensor zone 1010, certain regions of the uppersubstrate 905 that are directly below the ridges of the fingerprint maydeflect and cause the upper fingerprint electrodes 1020 to make contactwith the fixed resistors 1045 on the lower fingerprint electrodes 1040.This switch closure may be through a resistor, such as a large valueresistor, which can provide for distinguishing which of the many sensorelements are being pressed and which are not. Scanning rows or columnsof such a fingerprint sensor array can produce digital output thatrepresents the fingerprint ridges or absence of the same. Suchfingerprint sensor implementations can enable scanning of thefingerprint array and acquisition of a fingerprint image.

The use of the digital resistive technique for handwriting andfingerprint recognition can result in a fast scan rate. This is due inpart to the “digital” nature of the output from each cell during thescanning process, which can enable high frame rates for fingerprintcapture and handwriting recognition.

In some implementations, a force-sensitive membrane switch may be usedto locally connect an extra capacitor into a PCT measurement circuit,thus causing a large change in capacitance when the switch is closedwith applied pressure from, for example, a finger or a stylus tip. Theswitches may be formed near the intersections of sensor rows andcolumns. The extra capacitor may be formed in series with the switchusing conductive material to connect with row and column lines. In someimplementations, this capacitor can produce a large change incapacitance relative to the change in mutual capacitance of a PCT-onlyconfiguration.

One such implementation is depicted in FIGS. 13 and 14. FIG. 13 shows anexample of a top view of a force-sensitive switch implementation. FIG.13 indicates portions of two columns and two rows of such a combinedsensor device 900, wherein the column electrodes 1305 have a width 1310and a spacing or “pitch” 1315. The widths of the column and rowelectrodes are generally made small, on the order of a few microns, toimprove overall transparency of the combined sensor device. The pitchcan range from about 10-50 microns, suitable for fingerprint detection,to about 5 mm for lower resolution devices. Alternative implementationsmay have pitches of less than 50 microns or more than 5 mm. FIG. 14shows an example of a cross-section through a row of the force-sensitiveswitch implementation shown in FIG. 13.

In the implementation depicted in FIGS. 13 and 14, a capacitor 1317 isformed over the rows between the row electrodes 1335 and the capacitortop electrode 1320 in each sensel. A connection between the columnelectrodes 1305 and the capacitors 1317 may be made through a contact1325 at the intersection of the rows and columns, which may include afixed resistor in series with the contact. This contact 1325 may beelectrically connected to the capacitor top electrode 1320, forming anelectrode of a switch that may be open or closed. In some alternativeconfigurations there may be no separate contact 1325—physical contactmay be made directly between the column electrode 1305 and the capacitortop electrode 1320. The row electrodes 1335 may be disposed on asubstantially transparent lower substrate 910, which may be made of amaterial such as glass, plastic, etc. In some implementations, the othercomponents depicted in FIGS. 13 and 14 also may be substantiallytransparent.

In this example, a compressible layer 1025 is disposed between the uppersubstrate 905 and the capacitor top electrode 1320. The compressiblelayer 1025 may be an insulator that is formed of a material having asufficiently low elastic modulus that may be easily compressed and doesnot interfere with the switch to the capacitor. Here, the uppersubstrate 905 is a flexible membrane disposed on top of the sensor toprotect the surface and yet deflect locally when touched, in order toactuate the switches.

FIG. 15A shows an example of a circuit diagram that representscomponents of the implementation shown in FIGS. 13 and 14. In thecircuit 1500 a, a signal may be applied at the input 1505 and sensed bythe analog-to-digital converter (ADC) 1540. The signal may be modulatedby a change in mutual capacitance, C_(m), when a finger is on or nearthe flexible membrane. Such changes in C_(m) are represented by avariable capacitor 1525. The self-capacitances of rows and columns arerepresented by capacitors 1530 and 1535, respectively. The contacts atthe intersection of the rows and columns (see FIGS. 13 and 14) arerepresented as a switch 1510 having a resistance R1 represented by theresistor 1515 and a capacitance C1 represented by the series capacitor1520. The resistance R1 also may include the line resistance of thecorresponding row or column electrodes. When force (such as a touch) onthe flexible upper substrate 905 closes the switch 1510, capacitance C1is added to the mutual capacitance C_(m). In some implementations, C1 issubstantially larger than C_(m) because a touch can generally reduceC_(m) whereas closing the switch 1510 adds capacitance: when the switchis closed, the mutual capacitive effect of the touch may be masked bythe value of C1.

In one example, a high-resolution sensor may be formed having row andcolumn widths of 5 um and a pitch of 50 um between rows and columns (forexample, see FIGS. 13 and 14). If, for example, the capacitor insulator1330 is 1000 Å thick and formed of silicon nitride (SiN), and thecapacitor top electrodes 1320 cover a 40 um×5 um area (see FIG. 14), amodulation of greater than 60 femtofarads (fF) may be obtained using theparallel-plate capacitor equation C=e_(r)e_(o)A/d where e_(r) is therelative permittivity of the insulator, e_(o) is the permittivity offree space, A is the area of the top electrodes, and d is the thicknessof the dielectric. In some implementations, this can be consideredadequate for determination by PCT controller circuitry. Decreasing thelength or the width of the capacitor electrodes will decrease thecapacitance value, whereas decreasing the thickness of the dielectricinsulator will increase the capacitance. In some implementations, thecapacitance value can be made appreciably larger by spanning a portionof the sensel area between the row and column electrodes with thecapacitor top electrode or by increasing the row and column widths. Insome implementations, the value of the capacitance can be reduced byreducing the electrode width or the pitch of the sensel. By changing thedimensions of the capacitor electrodes and the thickness of theinsulator, values of capacitance in the range from less than about 10 fFto more than about 0.1 pF may be obtained.

FIG. 15B shows an example of a circuit diagram that representscomponents of an alternative implementation related to FIGS. 13 and 14.The circuit 1500 b can be used to consider the response times for asensor such as that depicted in FIGS. 13 and 14. Here, a leakageresistor 1545 having a resistance R2 has been added to the circuit toallow for the discharge of series capacitor 1520 when switch 1510 isopen. If, for example, R2 were 100 megaohms and R1 were 10 kilohms, thenthe frequency response (1/RC) for the C1 value for a 40 um×5 umcapacitor as described above would be a minimum of 150 KHz for aclosed-to-open transition of the switch 1510 and a maximum value of 1.5GHz to charge the capacitor though the series resistor 1515 when switch1510 is closed. The frequency response may be helpful in determining aminimum obtainable frame rate for the combination sensor. The frequencyresponse and frame rate may be increased, if needed, by decreasing theRC time constant with reductions to the resistor values R1 or R2 or withreductions in the capacitance.

In some implementations, the resistor 1515 represents the contactresistance of contact 1325 (e.g., no fixed resistor and no FSR). In someother implementations, the resistor 1515 represents the contactresistance directly between the column electrode 1305 and the capacitortop electrode 1320 as shown in FIG. 14 (e.g., no fixed resistor, no FSR,and no contact 1325). In some implementations, the resistor 1515 mayinclude the resistance of an additional fixed resistor such as avertical or serpentine fixed resistor (not shown) positioned between acontact 1325 and the capacitor top electrode 1320 in FIG. 14. The fixedresistor may include a thin-film conductive cap disposed thereon servingas the contact 1325 to aid in electrical contact with a column electrode1305. The resistor 1515 may include a force-sensitive resistor in serieswith a fixed resistor or in lieu of a fixed resistor. The resistor 1515may include an ohmic material such as a resistive or metal thin film.Alternatively, the resistor 1515 may include a non-linear device such asa leaky diode or other device. According to some implementations, theresistor 1515 may have a resistance ranging from less than a few ohms toover 100 megaohms. In some implementations, the leakage resistor 1545may have a value on the order of 100 kilohms or larger.

The switched capacitor configuration described with respect to FIGS. 13through 15B encompass what may be called digital capacitive touch (DCT),in that a local capacitor near the intersection of a row and a column ofa DCT sensor array can be digitally switched in or out, depending onwhether a force-actuated switch at the intersection is open or closed.The DCT array, in some configurations, may serve as a fingerprintsensor, a stylus or handwriting sensor, a touch sensor, or a combinationthereof without a corresponding PCT array. The DCT array, in some otherconfigurations, may be combined with a PCT array. In one suchconfiguration, one or more capacitive electrodes electrically connectednear each intersection between overlapping rows and columns in an arraysurround a force-actuated capacitive switch located at each intersection(for example, see FIG. 9B). The combined sensor array may use theforce-sensitive capacitive switch for stylus detection and the PCT arrayfor light touch or proximity sensing. As noted above, the same PCTdetection circuitry may be used for detecting the application of forceor pressure from the pressing of a stylus, pen or finger in the DCTaspect, as well as the light touch from a finger or stylus in the PCTaspect. As noted earlier, the designations regarding rows and columns,the manner of overlapping, the various aspect ratios, and other featuresare intended to be illustrative and not limiting. For example, the rowsand columns may be interchanged, the column electrodes may pass over orunder the row electrodes, and the pitch or resolution may be changedwithout loss of generality.

FIG. 16 shows an example of a flow diagram illustrating a manufacturingprocess for a combined sensor device. FIGS. 17A-17D show examples ofpartially formed combined sensor devices during various stages of themanufacturing process of FIG. 16. According to some implementations,block 1605 of the process 1600 involves depositing a substantiallytransparent conductor, such as ITO, on upper and lower substantiallytransparent substrates. In this example, the lower substrate 910 is aglass substrate. However, in alternative implementations, the lowersubstrate 910 may be formed of plastic or a similar material. Some suchimplementations can lend themselves to a roll-to-roll manufacturingprocess.

Block 1605 also may involve patterning the substantially transparentconductive material into electrodes, using photolithography and etchingprocesses or other “additive” processes such as plating, screenprinting, etc. In some implementations, this patterning process resultsin diamond electrode shapes (or other shapes as appropriate), connectedto one another within columns or rows patterned on the upper substrate905 and the lower substrate 910.

A resistive material may subsequently be deposited (e.g., by sputterdeposition) on at least some electrodes of the lower substrate 910 andon or connected to the patterned electrodes, as shown in block 1610. Inalternative implementations, resistive material may be deposited on atleast some electrodes of the upper substrate 905. The resistive materialmay be patterned to be in series with all or a subset of the sensinglocations on the electrodes. According to some implementations, theresulting resistors may have a resistance on the order of 1 megaohm;other implementations may produce resistors having a smaller or greaterresistance such as between 100 kilohm and 10 megaohm.

The electrodes and resistors may be patterned in at least two generalways, as shown in FIGS. 17A and 17B. A first option (top viewillustrated in FIG. 17A) is to form a serpentine resistor 1035 bypatterning the lower electrode material or other resistive materialdeposited on lower substrate 910 into a thin, narrow sequence of one ormore connected segments that conduct in the plane of the film to achievea sufficiently high resistance. A conductive contact region 1036 formedfrom the lower electrode material or other suitable material may beincluded at the end of the resistor 1035. A second option (side viewillustrated in FIG. 17B) is to pattern a vertical resistor 1035 directlyon top of the lower electrodes 1030, in which case the conduction pathis through the resistor in a direction substantially normal to the planeof the film. In some implementations, a thin metal contact region 1037may be included above the vertical resistor 1035.

Block 1615 of the process 1600 may involve depositing or otherwisedisposing the compressible layer 1025 on the lower substrate 910. Insome implementations, the compressible layer 1025 may be a patternable,thin (e.g., 1 to 10 microns) polymer with a low elastic modulus, such asan elastomer. In some implementations that include gaps in thecompressible layer 1025 (such as those discussed above with reference toFIGS. 10A-10C), the compressible layer 1025 may be patterned such thatthe regions above the resistors 1035 are opened up. FIG. 17C provides across-sectional view of a portion of a combined sensor device 900 thathas been partially fabricated according to one such example. In someother implementations, the regions above resistors 1035 that are openedup may be filled with a force-sensitive resistor material (not shown).In some other implementations with or without the FSR material, an uppersurface of vertical or serpentine resistors 1035 may be covered with athin metal layer.

At this stage of the process 1600, the compressible layer 1025 has beenpatterned to expose the lower electrodes 1030 on which the resistors1035 have been formed. In some implementations of the process 1600, FSRmaterial may be formed on fingerprint sensor electrodes of the lowersubstrate 910 (see optional block 1620), the handwriting and touchsensor electrodes of the lower substrate 910, or both. FIG. 10D providesan example of the force-sensitive resistor material 1085 formed on thelower fingerprint electrodes 1040. The force-sensitive material may beformed on the electrodes by methods such as dispensing, screening,depositing, or patterning. Force-sensitive resistor material also may beincluded on the handwriting and touch sensor electrodes of the lowersubstrate 910 (not shown).

Subsequent to the patterning and curing (if needed) of the compressiblelayer 1025, an additional thin layer of adhesive 1705 (such as ˜1-5microns) may be applied on the surface of the compressible layer 1025(see optional block 1625) to improve adhesion, taking care not to applythe adhesive on the top surface of the resistors 1035. Methods to applythe adhesive include photolithography, screen printing, squeegeeing, anddispensing. An example of such an adhesive layer 1705 may be seen inFIG. 17D.

FIG. 17D depicts the apparatus after the upper substrate 905 has beenjoined to the compressible layer 1025. The upper substrate 905 may beformed of a substantially transparent material and may havesubstantially transparent upper electrodes 1015 patterned on theunderside. The upper substrate 905 may, for example, be formed of aplastic film such as polyethylene terephthalate (PET), polyethylenenaphthalate (PEN), polyimide, or a similar material. In this example,the upper electrodes 1015 are made of ITO that has been formed into rowsthat are continuous in the plane of FIG. 17D. In alternativeimplementations, the upper electrodes 1015 as well as the lowerelectrodes 1030 may be patterned into similarly-shaped pads, connectedas rows or columns. In some implementations, the two substrates may bejoined by bringing the upper substrate 905 into alignment with the lowersubstrate 910 and attaching the layers via the adhesive 1705 that hasbeen applied over the compressible layer 1025. Other techniques may beused, such as hot pressing the two layers together, mechanical clampingthe periphery of the substrates, or an adhesive-free method.

Implementations such as those depicted in FIGS. 17C and 17D include airgaps in the compressible layer 1025 around the electrodes on whichresistors have been formed. Such air gaps are depicted in areas 1065 ofFIG. 17D. Air gaps can result in higher levels of undesirablereflectance from the air-substrate interfaces. Details are describedabove with reference to Equation 1. Accordingly, in someimplementations, the air gap regions may be spatially limited, so thatthe air gaps do not materially impact the overall optical transmissionof the stack. For example, the air gap regions may be limited to an areain the range of 1-5% of the total area of the sensor. Alternatively, theair gaps may be limited to the region of the fingerprint imaging areaonly, which may be a limited region of lower optical transmission, andtherefore may be on the cover glass but not directly above the displayarea.

In alternative implementations, such as the examples described withreference to FIGS. 10C and 10D, the compressible layer 1025 also may bedeposited on at least some of the lower electrodes 1030 on which theresistors 1035 have been formed. In some such implementations, there areno air gaps in the handwriting and touch sensor zone 1005. However,other electrodes on which resistors have been formed (such as in thefingerprint sensor zone 1010) may or may not have the compressible layer1025 deposited on them. In still other implementations, however, thefingerprint sensor zone 1010 may include no air gaps. As shown in FIG.10D, such implementations may include FSR material 1085 in thefingerprint sensor zone 1010. In some other implementations, the FSRmaterial 1085 also may be included above lower electrodes 1030 in thehandwriting and touch sensor zone 1005, with or without fixed verticalor serpentine resistors 1035.

Some implementations of the process 1600 involve a process flow withrelatively few masking steps. Some such implementations involve twomasking steps for depositing material on the lower substrate 910 and asingle masking step for depositing material on the upper substrate 905.Structures may be formed on at least the upper substrate 905 usingroll-to-roll manufacturing processes. For implementations wherein thelower substrate 910 is plastic or a similar material, a roll-to-rollmanufacturing process may be used for depositing material on the lowersubstrate 910. In such implementations, the lower substrate 910 may bethicker than the upper substrate 905. In some examples, the uppersubstrate 905 may be laminated onto the lower substrate 910 to form thesensor stacks described above. The resultant combined sensor device 900may be inexpensive, light, thin and highly suitable for mobile and otherhandheld electronic devices. In some implementations, this laminate ofan upper plastic layer and a lower plastic layer may be furtherlaminated onto or otherwise attached to a substantially transparent andrelatively more rigid substrate, such as a glass substrate. In someimplementations, the substantially transparent substrate may be adisplay substrate such as the transparent substrate 20 described above.

In this implementation, block 1635 involves processing and packaging.Block 1635 may involve the singulation of individual combined sensordevices 900 from large substrates such as large plates of glass or longrolls of plastic having multiple combined sensor devices 900 formedthereon by cutting, cleaving, sawing, or other suitable methods.Singulation of sensor devices from larger substrates may be performedprior to block 1635, such as prior to attaching the upper substrate (seeblock 1630) or prior to applying adhesive to the compressible material(see block 1625). Block 1635 may involve configuring combined sensordevices 900 for electrical communication with one or more sensorcontrollers, such as the combined sensor controller 77 described belowwith reference to FIG. 25B. Block 1635 may involve attaching combinedsensor devices 900 to a display device 40 such as described elsewhereherein. Block 1635 may involve packaging individual combined sensordevices 900 for shipment or storage.

FIG. 18A shows an example of a block diagram that illustrates ahigh-level architecture of a combined sensor device. In this example, amulti-touch sensor 1801, a high resolution handwriting sensor 1803, anda fingerprint sensor 1805 are integrated into the combined sensor device900. A cover glass included with the combined sensor device 900 can beoverlaid onto many displays, including but not limited to LCD, OLED andreflective displays. Some such displays may be displays suitable formobile devices and some may be suitable for other devices, such asconsumer electronic devices, depending on the implementation. Themulti-touch sensor 1801, such as a PCT sensor, and the high-resolutionhandwriting sensor 1803, such as a parallel-plate capacitivedisplacement sensor or a DRT sensor, may be interleaved at theintersection of rows and columns of an addressable sensor device asdescribed above with respect to FIGS. 9A and 9B and FIGS. 10A-10D. Thefingerprint sensor 1805 with even higher resolution may be included in apreselected region over a portion of the display area, such as in theexample shown in FIG. 12. Alternatively, the multi-touch sensor 1801 andthe high-resolution handwriting sensor 1803 may serve as a fingerprintsensor 1805 anywhere above the display area when the combined sensordevice has sufficient resolution.

In the example shown in FIG. 18A, the control system 1807 includes atleast one microcontroller 1809 and at least one application processor1810. In some implementations, hardware, software and/or firmware forall sensors of the combined sensor device 900 may be integrated on asingle microcontroller 1809, whereas in other implementations separatemicrocontrollers 1809 may be used for touch sensing, handwriting sensingand fingerprint sensing functionality. Applications for all sensors maybe integrated on a single application processor 1810 or on multipleapplication processors 1810. These processors may reside, for example,within a display device or within a mobile device.

Here, the sensors in the combined sensor device 900 communicate with themicrocontroller 1809, which in turn communicates with applicationprocessor 1810. The communication between these devices may go in bothdirections. In some implementations, the microcontroller 1809 drives thesensors of the combined sensor device 900 and receives sense data fromthe sensors. The application processor 1810 may be configured both tomonitor the output of the microcontroller 1809 and to send commands tothe microcontroller 1809. The microcontroller 1809 may, for example, belocated on the lower substrate 910, on an attached flex cable, or on anelectrically connected printed circuit board. In some implementations,the microcontroller 1809 also may be configured to control a displayand/or to perform other functions.

Some implementations may be provided via application software stored inone or more tangible, machine-readable media. Such media may be part ofthe applications processor 1810 or may be separate media accessible bythe applications processor 1810. The application software may includeinstructions for controlling one or more devices to perform variousfunctions. For example, the application software may includeinstructions to activate the fingerprint sensor zone 1010 forfingerprint sensing only when fingerprint sensing is needed. Otherwise,the fingerprint sensor zone 1010 may be de-activated or activated formulti-touch and/or handwriting functionality, depending on theimplementation.

Alternatively, or additionally, the application software may includeinstructions to reduce power consumption by turning off sensors, turningoff parts of the microcontroller 1809 and/or employing first-levelscreening at a reduced frame rate on a low-resolution sensor beforeactivating power-hungry higher-resolution sensors. For example, theapplication software may include instructions for reducing powerconsumption by aggregating sensels (or aggregating rows or columns ofthe combined sensor device 900) electronically using the microcontroller1809, so that the combined sensor device 900 performs at a lowerresolution and may consume less power and provide a higher signal untilhigher resolution is needed.

In some implementations, the combined sensor device 900 can beconfigured to function in either a touch mode or a handwriting mode(which also may be referred to herein as a stylus mode), instead ofbeing configured to function in both modes simultaneously. It may beadvantageous not to have the combined sensor device 900 function in bothmodes simultaneously. For example, when a user is writing on thecombined sensor device 900 with a stylus, it may be preferable to avoidsensing the user's palm or fingers that also may be resting on thedevice. Operating the combined sensor device 900 to function as ahandwriting sensor may influence and/or interfere with the combinedsensor device 900's functionality as a touch sensor, and vice versa.Accordingly, some implementations provide separate drive and/or sensesubsystems for touch and handwriting mode functionality. Someimplementations provide drive and/or sense subsystems that may beswitched quickly between touch mode functionality and handwriting modefunctionality.

FIG. 18B shows an example of a block diagram that illustrates a controlsystem for a combined sensor device. In this example, the control system1807 includes a stylus drive circuit 1811 and a touch drive circuit1813. When the combined sensor device 900 is being operated in ahandwriting mode, the stylus drive circuit 1811 sends one or more drivesignals 1814 to the handwriting and touch sensor zone 1005. When thecombined sensor device 900 is being operated in a touch mode, the touchdrive circuit 1813 sends the drive signals 1814 to the handwriting andtouch sensor zone 1005. However, in some alternative implementations,the drive signals 1814 are substantially the same whether the combinedsensor device 900 is being operated in a handwriting mode or in a touchmode.

In this example, the control system 1807 includes a stylus sense circuit1815 and a touch sense circuit 1817. When the combined sensor device 900is being operated in a handwriting mode, the stylus sense circuit 1815processes one or more sense signals 1818 from the handwriting and touchsensor zone 1005. When the combined sensor device 900 is being operatedin a touch mode, the touch sense circuit 1817 processes the sensesignals 1818 from the handwriting and touch sensor zone 1005. In someimplementations, the control system 1807 may include a single circuitthat can be switched from a touch configuration to a handwritingconfiguration. Some examples are described below.

FIG. 18B also shows an example of a circuit diagram representingcomponents of a sensel 1819 in the handwriting and touch sensor zone1005. In this enlarged view of the sensel 1819, the resistance of aswitch 1823 is schematically depicted, as well as the mutual capacitance1824 between associated electrodes of the sensel 1819.

FIG. 18C shows an example representation of physical components andtheir electrical equivalents for a sensel in a combined sensor device.In this example, the sensel 1819 includes a switch 1823 formed in anoverlapping region between a drive electrode 1820 and a sense electrode1821. The switch 1823 is represented by a switch capacitance 1826 and aleakage resistance 1828 positioned between the drive electrode 1820 andthe sense electrode 1821 that accounts for small amounts of leakagecurrent that can flow through switch 1823 when the switch is open. Theleakage resistor 1828 may have a value on the order of 1 megaohms orlarger. A fixed resistor 1822 may be positioned between the driveelectrode 1820 and the sense electrode 1821, electrically connected inseries with the contacts of the sensel switch 1823. The fixed resistor1822 may be a serpentine resistor, a vertical resistor, ahigh-resistivity film, a leaky diode, or other linear or non-linearresistive element. The fixed resistor 1822 may be in the range of ahundred kilohms to 10 megaohms or larger. In this example, the switch1823 includes a serpentine fixed resistor 1822, which may be similar tothe configuration depicted in FIG. 17A.

When the finger 1047, a stylus, etc., presses on the switch 1823,portions of the drive electrode 1820 are brought closer to the senseelectrode 1821, increasing a parallel capacitance 1832 between the driveelectrode 1820 and the sense electrode 1821. A sufficiently high appliedpressure or force will close the switch 1823. The proximity of thefinger 1047, a conductive stylus, etc., also may result in a change ininter-electrode mutual capacitances 1824 between adjacent driveelectrodes 1820 and sense electrodes 1821.

FIG. 18D shows an example of an alternative sensel of a combined sensordevice. The configuration shown in FIG. 18D is similar to that of FIG.9B, which is described above. In this example, the drive electrodes 1820and the sense electrodes 1821 include diamond-shaped sections 1825 andnarrow portions 1827. In this example, the switches 1823 are formed inthe overlapping regions 925 b (see also FIG. 9B).

The parallel capacitance 1832 is formed between the drive electrode 1820and the sense electrode 1821 in the overlapping regions 925 b. The totalmutual capacitance of the sensel 1819 is equal to the sum of each of theindividual inter-electrode mutual capacitances 1824 between adjacentdrive electrodes 1820 and sense electrodes 1821. In this example, thetotal mutual capacitance is about four times the inter-electrode mutualcapacitance. Each of the diamond-shaped sections 1825 of the driveelectrodes 1820 has a sensel drive resistance 1853 and each of thediamond-shaped sections 1825 of the sense electrodes 1821 has a senselsense resistance 1854.

FIG. 18E shows an example of a schematic diagram representing equivalentcircuit components of a sensel in a combined sensor device. The axis1829 represents various levels of applied drive signals, such as thedrive signals 1814 from the stylus drive circuit 1811 or the touch drivecircuit 1813 (for example, see FIG. 18B). The axis 1831 representsvarious levels of responsive sense signals, e.g., the sense signals 1818to the stylus sense circuit 1815 or the touch sense circuit 1817 of FIG.18B.

Mutual capacitance component 1833 may represent the mutual capacitancebetween the drive electrodes 1820 and the sense electrode 1821 and thechanges caused by the proximity of the finger 1047, as shown in FIG.18C. Parasitic capacitance component 1835 represents self-capacitance ofan electrode, such as sense electrode 1821 of FIG. 18C, and the changescaused by the proximity of the finger 1047 or of another conductivebody. Parallel capacitance component 1836 represents the parallel-platecapacitance, and changes such as that caused by the pressure of finger1047, a stylus, etc., causing the drive electrode 1820 to be movedcloser to the sense electrode 1821 of FIG. 18C. The position of theswitch 1823 represents the closure or non-closure of the switch 1823. Inone example, mutual capacitance component 1833 has a value of about 0.5pF; parasitic capacitance component 1835 has a value between about 0.5pF and 20 pF; parallel capacitance component 1836 has a value of about0.5 pF; and switch 1823 has a value of about 10 gigaohm when open andabout 1 kilohm when closed. A person having ordinary skill in the artwill readily understand that other capacitance and resistance values arealso possible depending on the desired implementation. In somealternative implementations, the switch 1823 will have a value of lessthan 100 ohms (such as when the fixed resistor is omitted) when closed.In some other implementations, the switch 1823 will have a valueeffectively equal to the fixed resistor when closed.

Some implementations described herein provide a single circuit that canbe switched between a touch mode configuration and a handwriting modeconfiguration. For example, a single circuit may be configured toperform the functions of the stylus sense circuit 1815 and the touchsense circuit 1817 of FIG. 18B.

FIG. 18F shows an example of an operational amplifier circuit for acombined sensor device that may be configured for handwriting or stylusmode sensing. When operating in handwriting mode, the circuit 1837 isconfigured to function as an integrator with reset capability. Thecircuit 1837 may be configured to generate relatively large outputvoltages from the relatively small input currents that result fromhandwriting sensing of the combined sensor device 900 when one or moreswitches 1823 are closed.

In this example, the circuit 1837 includes an operational amplifier1839, a feedback capacitor 1841 and a feedback resistor 1843, as well asswitches 1842 and 1844. In one example, the feedback capacitor 1841 hasa value between about 6 pF and 20 pF, and the feedback resistor 1843 hasa value of about 5 megaohm or higher. However, the circuit 1837 may beimplemented with other capacitance and resistance values and have otherconfigurations that provide similar functionality. For example,alternative implementations may include a transistor (such as a metaloxide semiconductor field effect transistor (MOSFET)) operating in theoff state instead of feedback resistor 1843. Instead of the switch 1842,some implementations may include a lossy device such as a high-valueresistor or an NMOS or PMOS transistor with a known resistance.Moreover, some implementations may include an additional resistor inseries with the switch 1842.

When operating in the stylus mode, the switch 1844 can be left open andthe switch 1842 can be opened and closed. The graphs 1845, 1847 and 1849show examples of steady-state input current operation. The graph 1845indicates input current over time. In this example, the current is heldconstant at a steady-state value I_(ss). At time t₁, the switch 1842 isopened. Referring to the graph 1847, it may be seen that to open switch1842, the voltage applied to switch 1842 is changed to switch openvoltage 1848. The switch open voltage 1848 may vary according to theparticular implementation. In some implementations, the switch openvoltage 1848 may be 1.8V, whereas in other implementations the switchopen voltage 1848 may be 3.3V, 5V, 10V, 20V or some other voltage.

The graph 1849 indicates the output voltage that results from openingthe switch 1842. In this example, because the input current is constant,the output voltage 1850 a increases linearly between time t₁, when theswitch 1842 is opened, and time t₂, when the switch 1842 is closedagain. The time interval (t₂−t₁) during which the switch 1842 is openmay be, for example, on the order of 0.1 to 10 μsec, or even less. Inthis example, the output voltage 1850 a reaches a maximum output voltage1851. Here, the maximum output voltage 1851 is opposite in sign from theswitch open voltage 1848 and has a lower absolute value than the switchopen voltage 1848. When the switch 1842 is closed (at time t₂), thecapacitor 1841 may be discharged and the output voltage 1850 a is reset.

FIG. 18G shows an example of the operational amplifier circuit of FIG.18F configured for touch mode sensing. In this configuration, the switch1844 is closed, which allows the circuit 1837 to function as a chargeamplifier for detecting changes in mutual capacitance C_(m) betweenadjacent drive electrodes 1820 and sense electrodes 1821 (for example,see FIGS. 18C and 18D). In this example, drive signal 1852 is a squarewave having a voltage V_(drv).

An example of the resulting output voltage 1850 b is shown in FIG. 18G.The output voltage 1850 b is not a linear response like that of theoutput voltage 1850 a, but instead is an inverted and non-linearresponse to the leading and trailing edges of the drive signal 1852.This response follows from the basic relationship between the currentinto a capacitor I=C dV/dt, where I is the current, C is the capacitanceof the capacitor and dV/dt is the derivative of voltage with respect totime.

A PCT sensor can exhibit shorted sensels when, for example, a sensel ispressed with a finger or a stylus and the sensel switch is closed. Thiscondition has the potential to create larger-than-normal signals thatcan saturate the operational amplifier 1839 of the circuit 1837. While asaturated state can be sensed and identified, saturation recovery timecan be problematic for array sensing systems. Amplifier recovery time isusually not known with a high degree of confidence, typically beingcharacterized in a testing facility. If the operational amplifier 1839remains saturated, subsequent sensel measurements may be corrupted.Thus, recovery time can have a significant impact on the achievable scanrate of a sensor array.

In addition, the circuit 1837 may have feedback components with largetime constants that also can contribute to a long recovery period. Insome implementations, the circuit 1837 may include a large feedbackresistor (such as the resistor 1843) to provide DC feedback to stabilizethe circuit 1837. A large feedback resistor in parallel with thecapacitor 1841 can create a larger time constant that can inhibit sensorscan rates.

Accordingly, some implementations of the circuit 1837 are configured toinhibit or prevent saturation of the operational amplifier 1839. Somesuch implementations provide a low-impedance path to bleed off charge ofthe capacitor 1841, allowing for fast re-set of the circuit 1837 and/orfast recovery from a saturated state of the operational amplifier 1839.

FIG. 18H shows an example of an operational amplifier circuit for acombined sensor device that includes a clamp circuit. The clamp circuit1855 may be configured to inhibit or prevent saturation of theoperational amplifier 1839 by limiting the output voltage of the circuit1837. In this example, the clamp circuit 1855 is disposed in parallelwith other components of the circuit 1837.

FIG. 18I shows examples of clamp circuit transfer functions. Thefunction 1857 is an ideal clamp circuit transfer function, whereas thefunction 1859 is an example of an actual clamp circuit transferfunction. Both of the functions 1857 and 1859 indicate a very highimpedance while the clamp circuit 1855 is operating within the clampvoltage range (V_(c−)<V_(o)<V₊). The clamp circuit 1855 may beconfigured with clamp voltages V_(c−) and V_(c+) with absolute valuesthat are less than those of the corresponding saturation voltagesV_(sat−) and V_(sat+).

Within the clamp voltage range, the circuit 1837 can operate in a touchmode with little or no influence from the clamp circuit 1855. When theoperational amplifier is “clamped” (when V_(out) reaches or exceedsV_(c+) or V_(c−)), the impedance of the clamp circuit 1859 is very low,as shown by the significant increase in the absolute value of I_(out).If the impedance of the clamp circuit 1855 is made very low, thisessentially shorts the feedback components of the circuit 1837, therebyallowing the feedback capacitor 1841 to discharge (see FIG. 18H).

FIG. 18J shows an example of a circuit diagram for a clamp circuit. Inthe configuration depicted in FIG. 18J, the clamp circuit 1855 includesn diodes 1861 arranged in series and having a first forward direction.The diodes 1861 are disposed in parallel with the diodes 1863. In thisexample, there are n diodes 1863 arranged in series and having a secondforward direction that is opposite to that of the diodes 1861. In someimplementations, the forward voltage of each of the diodes 1861 and 1863may be on the order of 1V or less, e.g., 0.2V, 0.3V or 0.6V. The valueof n, as well as the forward voltage of the diodes 1861 and 1863, mayvary according to the implementation. The clamp circuit transferfunction of a clamp circuit 1855 having a relatively larger number ofdiodes, each with a relatively lower forward voltage, will approximatean ideal clamp circuit transfer function more closely than a clampcircuit 1855 having a relatively smaller number of diodes, each with arelatively higher forward voltage.

However, the clamp circuit 1855 may be configured in various other ways.In some alternative implementations, at least one of the diodes 1861 and1863 may be a Zener diode. In some such implementations, one of thediodes 1861 is a Zener diode having a first forward direction and one ofthe diodes 1863 is a Zener diode having a second and opposing forwarddirection. In some such implementations, each of the Zener diodes may bepaired, in series, with a Schottky diode having an opposing forwarddirection. In some implementations, the Schottky diodes may have forwardvoltage drops of about 0.2V or 0.3V. The Zener breakdown voltage of thecorresponding Zener diodes may be substantially higher. For example, ina ±5V analog system, the Zener breakdown voltage may be 4.2V in oneimplementation.

In some implementations described herein, the lower substrate may format least a portion of the cover glass apparatus of a display device. Insome such implementations, the signal lines may be formed on the uppersurface of the cover glass, rather than underneath the cover glass. Sucha configuration has implications for the design of the sensing elementsin the array, because these elements may be routed outside the array andattached to integrated circuits (ICs) that are configured to address andsense the signals from the various sensing elements in the array.

Previous approaches (such as covering these routing wires or attachingICs on the top side of the cover glass and covering them with blackborder epoxy) may not be optimal. One reason is that the epoxy mayresult in topography on the touch surface that may be felt by the user.

Accordingly, some implementations described herein provide novel routingconfigurations. Some implementations involve the use of a flexible uppersubstrate 905 of a combined sensor device 900 as a platform for directattachment of one or more ICs, including but not limited to ASICs. Theflexible upper substrate 905 may be wrapped around the edge of the lowersubstrate 910 (the edge of a glass substrate or another suchsubstantially transparent substrate). Some such implementations involvewrapping the sensing wires and routing leads, and attaching ICs to theseleads in a manner that enables the cover glass to extend all the way tothe edge of a mobile display device, such as a smart phone device. TheIC(s) may be directly attached to the wrap-around portion of the uppersubstrate 905, thus enabling a minimal edge border on the device,eliminating or minimizing the need for a bezel, and reducing cost byintegrating the cover layer and flexible printed circuit. Some suchimplementations may not result in a topography that can be felt by auser.

Some examples will now be described with reference to FIGS. 19 through21B. FIG. 19 shows an example of a cross-section of a portion of analternative combined sensor device. In this implementation, the lowersubstrate 910 is formed of glass and the upper substrate 905 is formedof a flexible and substantially transparent material, such as a clearpolyimide. Here, conductive material (metallization in this example) hasbeen patterned into the upper electrodes 1015 on the upper substrate905. The upper electrodes 1015 on the underside of the upper substrate905 may be used to route the sensor's signal lines. The portion 1910 ofthe upper substrate 905 (which is not drawn to scale) may be configuredto wrap around the edge of the lower substrate 910 in someimplementations, such as the implementation shown in FIG. 21B. In theexample shown in FIG. 19, the lower electrodes 1030 on the lowersubstrate 910 may be bonded electrically to upper electrodes 1015 orother electrical traces or circuitry on the upper substrate 905 using ananisotropic conductive film (ACF) 1905 or a similar connection scheme.

FIG. 20 shows an example of a top view of routing for a combined sensordevice. The combined sensor device 900 illustrated in FIG. 20 includesboth flex-on-glass (FOG) 2005 and chip-on-flex (COF) 2010 aconfigurations. FIG. 20 also indicates the handwriting and touch sensorzone 1005 and the fingerprint sensor zone 1010 of the combined sensordevice 900. A ground ring 2015 may be included around portions of thehandwriting, touch and fingerprint sensor zones 1005 and 1010 to isolatenoise coupling from the system and to minimize false touches. Whilefingerprint sensor zone 1010 is shown as physically distinct fromhandwriting and touch sensor zone 1005, in some implementations withsufficiently high resolution in the handwriting and touch zone, the twozones merge and are indistinguishable. Software may be used to allocatea portion of the combined sensor device 900 for fingerprint detection.When combined with an underlying display device, the software may beused to display a box or other suitable designator for prompting a userwhere (and when) to place a finger on the sensor device.

FIG. 21A shows an example of a cross-sectional view of the devicethrough the combined sensor device shown in FIG. 20. In this example,the upper substrate 905 is bonded to the lower substrate 910 with theadhesive layer 1705. An additional COF 2010 b may be seen in this viewof the combined sensor device 900. Additional components such as passivedevices (not shown) and connective traces for signals, power, ground,and external connectors may be included on an extended portion of theupper substrate 905 along with a controller or other integrated circuitssuch as COF 2010 a and 2010 b. Electrical or connective vias (not shown)may be included in the flexible upper substrate 905 to aid inconnectivity of any electrical and electronic components. A stiffener2120 such as a Kapton® tape may be attached to an extended portion ofupper substrate 905.

FIG. 21B shows an example of a cross-sectional view of a wrap-aroundimplementation. In the combined sensor device 900 illustrated in FIG.21B, the flexible upper substrate 905 is wrapped around the edge of thelower substrate 910. FIG. 21B depicts the connection of IC 2105, whichis an ASIC in this example, to the upper electrodes 1015 on the inside(lower side) of the upper substrate 905. The IC 2105 may, for example,be configured for controlling the combined sensor device 900 to providetouch sensor, handwriting sensor and/or fingerprint sensorfunctionality. An electrical connector 2110 is attached to the upperelectrodes 1015 or to other traces on one or both sides of uppersubstrate 905 in this example. A bezel 2115 is shown in FIG. 21B.However, other implementations may not include the bezel 2115.

Here, the signal lines that address the electrodes on the lowersubstrate 910 are routed and connected to corresponding upper electrodes1015 on the underside of the flexible upper substrate 905. According tosome such implementations, both the cost and the complexity of thecombined sensor device 900 may be reduced by integrating thefunctionality of the flexible upper substrate 905 with that of aflexible printed circuit.

Using devices such as those described above, an array of applicationscan be enabled. Some such implementations involve using a mobilehandheld device as a user authentication-based secure gateway to enabletransactions and/or physical access. Some implementations involve usinga fingerprint sensor as part of a user authentication system, such asfor commercial or banking transactions. In some implementations, ahandwriting input function may be used for signature recognition andrelated applications. Alternatively, or additionally, someimplementations involve using the handwriting input feature toautomatically capture notes and stylus input from people in anenterprise, such as students an educational setting, employees in acorporate setting, etc.

For example, there is a growing trend to enable use of a mobile devicefor commercial transactions, in a manner similar to that in which acredit card is used. In this usage model, a user may simply input a PINnumber into a cellular telephone that is equipped with a communicationinterface such as Near Field Communication (NFC) configured tocommunicate with payment terminals.

One challenge with this model is that of user authentication. PINS andpasswords may be ineffective for preventing unauthorized access. Astolen mobile device or cellular telephone could result in improperusage of the device or phone for credit or debit transactions.

Some implementations provided herein relate to the use of a built-infingerprint sensor, such as the fingerprint sensor of the combinedsensor device 900, to enable local user authentication. FIG. 22 shows anexample of a flow diagram illustrating a fingerprint-based userauthentication process. The process 2200 may involve using a cellulartelephone as a fingerprint-based user authentication system to enabletransactions and/or physical access.

According to some such implementations, the user may be enrolled on amobile device, such as a cellular telephone, by providing one or morefingerprints. In some such implementations, the mobile device includes acombined sensor device 900. Alternatively, or additionally, the user mayprovide handwriting data. The fingerprint and/or handwriting data may beencrypted and stored securely within the mobile device. However, somealternative implementations provide for authentication by a remotedevice, such as a server. Such implementations may involve storing thefingerprint and/or handwriting data in a remote device. Moreover, someimplementations involve acquiring fingerprint and/or handwriting datafrom more than one person, so that more than one person may beauthenticated using the same mobile device.

During an authentication process, the user provides fingerprint and/orhandwriting data to the mobile device, such as through one or moresensors integrated in a cover glass apparatus of the mobile device(block 2205). The user may do so, for example, when the user wishes tomake a commercial transaction using the mobile device. The obtainedfingerprint and/or handwriting data may be processed securely, eitherwithin the mobile device or via a remote device such as anauthentication server, and compared to the previously enrolled andstored fingerprint and/or handwriting data (block 2210). In block 2210,the mobile device or the authentication server determines whether thereis a match between the obtained fingerprint and/or handwriting data andthe stored fingerprint and/or handwriting data.

If and only if there is a match will the transaction be permitted. If nomatch is found in block 2215, the process 2200 may allow the user to tryagain, e.g., for a limited number of times (block 2220). If the usercannot provide matching fingerprint and/or handwriting data within thisnumber of times, the process may end (block 2230). In someimplementations, the mobile device or the authentication server may senda notification to, e.g., a financial institution and/or to localgovernmental authorities if improper data is received. In this example,either the mobile device or the authentication server is configured tosend an authorization signal to another device if the transaction ispermitted (block 2225). Examples of such devices include the mobiledevice 40 and the payment terminal 2310 shown in FIG. 23A.

FIG. 23A shows an example of a mobile device that may be configured formaking commercial transactions. In this example, the mobile device is afingerprint-secured cellular telephone that is configured for wirelesscommunication with the payment terminal 2310, such as via NFC. Thecellular telephone is an instance of the display device 40, describedelsewhere herein, and may include a combined sensor device 900 such asthat described above. Alternatively, the cellular telephone may includea fingerprint sensor zone 1010 that is not part of a combined sensordevice 900.

According to some implementations, a user may provide fingerprint datato the mobile device according to a process such as that described abovewith reference to FIG. 22. If there is a match between the stored andrecently-provided fingerprint data, the transaction can be permitted.For example, the payment terminal 2310 of FIG. 23A may send a signal toa corresponding device of a financial institution indicating that apayment should be authorized. The financial institution may or may notapprove the payment, depending on factors such as the availability offunds or credit. FIG. 23A shows a mobile device used to authorize apayment at a payment terminal in physical proximity to the phone. Insome other implementations, the mobile device can be used to authorizepayments made remotely, such as an e-commerce transaction made via a webbrowser or other application running on the mobile device, or toauthorize a payment made through a separate system, such as ane-commerce transaction made via a web browser or other applicationrunning on a personal computer under the control of a user. Referring toFIGS. 22 and 23A, the authorization signal of block 2225 can be used tocontrol the release of data on the mobile device itself, such as acontrol bit to authorize transmission of payment or credit cardinformation to payment terminal 2310. In another implementation, theauthorization signal of block 2225 may be sent to another device orprocess server, such as a device or server of a financial institutionindicating that a payment should be authorized.

Many physical facilities in corporate and government locations aresecured electronically, and are accessed using wireless radio frequencyidentification (RFID) cards, key fobs, etc., that operate on specificwireless frequencies, such as 128 kHz. These are short-range devicesthat draw energy by inductively coupling power from a card reader or asimilar device located near a door. If an RFID card or key fob fallsinto the wrong hands, security could be compromised at these accesspoints.

Instead of using a separate RFID card or key fob, some implementationsinvolve the use of a fingerprint-secured mobile device, such as afingerprint-secured cellular telephone, to gain access to such physicalfacilities. FIG. 23B shows an example of using of a fingerprint-securedmobile device for physical access applications. The mobile device is aninstance of the display device 40, described elsewhere herein, and mayinclude a combined sensor device 900.

In some such implementations, a fingerprint-secured mobile device may beused for opening an NFC-enabled access point 2320, such as a door 2315of a building, an automobile, a locker, a safe, etc., that may beelectronically locked. In some implementations, the access point may beconfigured for communication with other devices, such as anauthentication server, via a network. The fingerprint sensor zone 1010of the mobile device 40 may be used to implement (at least in part) anauthentication process for the user before the mobile device 40initiates its communications with the access point 2320. Theauthentication procedure may be similar to that described above for thesecure payment gateway; however, the application enabled is that ofphysical access, rather than a transaction.

Mobile devices are becoming a ubiquitous means for storage,transmission, and playback of documents, music, videos, and otherdigital assets. In order to preserve digital and other rights, and toprevent unauthorized access, distribution and copying of such digitalassets, some implementations involve the use of a fingerprint sensorand/or a handwriting sensor to be “married” to the asset in question. Inthis manner, only the person (or persons) authorized to access thedigital asset can access the asset through the use of the fingerprintsensor and/or the handwriting sensor, which may be sensors of a combinedsensor device 900 described herein.

In many enterprises, including corporate, government, educational andother settings, it may be beneficial to have an individual write noteson the screen of a mobile device. A device such as a tablet with a largescreen can substitute as a notepad, allowing meeting notes, interactivediscussions between colleagues and other important discoveries to beautomatically captured. One such device is depicted in FIG. 24A.

FIG. 24A shows an example of a secure tablet device. The tablet device2400 a of FIG. 24A may be configured for wireless communication with anetwork, such as a network maintained by an enterprise. The tabletdevice 2400 a may include a combined sensor device 900 such as describedelsewhere herein. Such network communications can facilitate storage ofinformation captured by the tablet device 2400 a on an enterprise'sdatabase of documents. Due to the often confidential and private natureof the information contained within these devices, access to suchtablets and phones should be restricted only to the authorized user(s).Otherwise, loss of such devices can result in unauthorized usage andcompromise of the data contained within.

Some such implementations provide access control according to ahandwriting recognition process and/or a fingerprint recognitionprocess. Access to the tablet device 2400 a may be controlled accordingto an analysis of a user's handwriting on the tablet device 2400 aand/or according to fingerprint data received from a fingerprint sensorprovided on the cover glass apparatus, as described above. In theexample depicted in FIG. 24A, the stylus tip 1105 can be used to providethe handwriting data 2410 via the tablet device 2400 a. Such data may beused for an authentication process similar to that described above withreference to FIG. 22.

FIG. 24B shows an example of an alternative secure tablet device. Thescreen of the tablet device 2400 b illustrated in FIG. 24B may act asthe handwriting input device or notepad. The tablet device 2400 b mayinclude a combined sensor device 900 such as described elsewhere herein.As shown in FIG. 24B, access to the tablet device 2400 b may becontrolled according to a handwriting authentication procedure: here,the stylus tip 1105 can be used to provide the handwriting data 2410.Alternatively, or additionally, access to the tablet device 2400 b maybe controlled according to a fingerprint authentication procedure usingfingerprint data acquired via the fingerprint sensor zone 1010. Thetablet device 2400 b may or may not be configured for finger touchsensing, depending on the particular implementation. Information may beautomatically captured on the screen and, in some implementations, maybe wirelessly synchronized with an enterprise's database. Alternatively,or additionally, such data can be stored locally. Some such data maysubsequently be synchronized with the enterprise's database, such asthrough a wired or wireless interface.

FIGS. 25A and 25B show examples of system block diagrams illustrating adisplay device that includes a combined sensor device. The displaydevice 40 can be, for example, a smart phone, a cellular phone, or amobile telephone. However, the same components of the display device 40or slight variations thereof are also illustrative of various types ofdisplay devices such as televisions, tablets, e-readers, hand-helddevices and portable media players.

The display device 40 includes a housing 41, a display 30, a combinedsensor device 900, an antenna 43, a speaker 45, an input device 48, anda microphone 46. The housing 41 can be formed from any of a variety ofmanufacturing processes, including injection molding, and vacuumforming. In addition, the housing 41 may be made from any of a varietyof materials, including, but not limited to: plastic, metal, glass,rubber, and ceramic, or a combination thereof. The housing 41 caninclude removable portions (not shown) that may be interchanged withother removable portions of different color, or containing differentlogos, pictures, or symbols.

The display 30 may be any of a variety of displays, including abi-stable or analog display, as described herein. The display 30 alsocan be configured to include a flat-panel display, such as plasma, EL,OLED, STN LCD, or TFT LCD, or a non-flat-panel display, such as a CRT orother tube device. In addition, the display 30 can include aninterferometric modulator display, as described herein. The combinedsensor device 900 may be a device substantially as described herein.

The components of the display device 40 are schematically illustrated inFIG. 25B. The display device 40 includes a housing 41 and can includeadditional components at least partially enclosed therein. For example,the display device 40 includes a network interface 27 that includes anantenna 43 which is coupled to a transceiver 47. The network interface27 may be a source for image data that could be displayed on the displaydevice 40. Accordingly, the network interface 27 is one example of animage source module. The transceiver 47 is connected to a processor 21,which is connected to conditioning hardware 52. The conditioninghardware 52 may be configured to condition a signal (e.g., filter asignal). The conditioning hardware 52 is connected to a speaker 45 and amicrophone 46. The processor 21 is also connected to an input device 48and a driver controller 29. The driver controller 29 is coupled to aframe buffer 28, and to an array driver 22, which in turn is coupled toa display array 30. In some implementations, a power supply 50 canprovide power to substantially all components in the particular displaydevice 40 design.

In this example, the display device 40 also includes a combined sensorcontroller 77. The combined sensor controller 77 may be configured forcommunication with the combined sensor device 900 and/or configured forcontrolling the combined sensor device 900. The combined sensorcontroller 77 may be configured to determine a touch location of afinger, a conductive or non-conductive stylus, etc., proximate thecombined sensor device 900. The combined sensor controller 77 may beconfigured to make such determinations based, at least in part, ondetected changes in capacitance in the vicinity of the touch location.The combined sensor controller 77 also may be configured to function asa handwriting sensor controller and/or as a fingerprint sensorcontroller. The combined sensor controller 77 may be configured tosupply touch sensor, handwriting sensor, fingerprint sensor and/or userinput signals to the processor 21.

Although the combined sensor controller 77 is depicted in FIG. 25B asbeing a single device, the combined sensor controller 77 may beimplemented in one or more devices. In some implementations, separatesensor controllers may be configured to provide touch, handwriting andfingerprint sensing functionality. Such sensor controllers may, forexample, be implemented in separate integrated circuits. In some suchimplementations, the addressing and/or measurement circuitry for touchmode, handwriting mode and/or fingerprint sensing mode may be containedwithin one or more controller or driver ASIC chips. In some alternativeimplementations, however, the processor 21 (or another such device) maybe configured to provide some or all such sensor controllerfunctionality.

The network interface 27 includes the antenna 43 and the transceiver 47so that the display device 40 can communicate with one or more devicesover a network. The network interface 27 also may have some processingcapabilities to relieve, for example, data processing requirements ofthe processor 21. The antenna 43 can transmit and receive signals. Insome implementations, the antenna 43 transmits and receives RF signalsaccording to the IEEE 16.11 standard, including IEEE 16.11(a), (b), or(g), or the IEEE 802.11 standard, including IEEE 802.11a, b, g, n, andfurther implementations thereof. In some other implementations, theantenna 43 transmits and receives RF signals according to the BLUETOOTHstandard. In the case of a cellular telephone, the antenna 43 isdesigned to receive code division multiple access (CDMA), frequencydivision multiple access (FDMA), time division multiple access (TDMA),Global System for Mobile communications (GSM), GSM/General Packet RadioService (GPRS), Enhanced Data GSM Environment (EDGE), TerrestrialTrunked Radio (TETRA), Wideband-CDMA (W-CDMA), Evolution Data Optimized(EV-DO), 1 xEV-DO, EV-DO Rev A, EV-DO Rev B, High Speed Packet Access(HSPA), High Speed Downlink Packet Access (HSDPA), High Speed UplinkPacket Access (HSUPA), Evolved High Speed Packet Access (HSPA+), LongTerm Evolution (LTE), AMPS, or other known signals that are used tocommunicate within a wireless network, such as a system utilizing 3G or4G technology. The transceiver 47 can pre-process the signals receivedfrom the antenna 43 so that they may be received by and furthermanipulated by the processor 21. The transceiver 47 also can processsignals received from the processor 21 so that they may be transmittedfrom the display device 40 via the antenna 43.

In some implementations, the transceiver 47 can be replaced by areceiver. In addition, in some implementations, the network interface 27can be replaced by an image source, which can store or generate imagedata to be sent to the processor 21. The processor 21 can control theoverall operation of the display device 40. The processor 21 receivesdata, such as compressed image data from the network interface 27 or animage source, and processes the data into raw image data or into aformat that is readily processed into raw image data. The processor 21can send the processed data to the driver controller 29 or to the framebuffer 28 for storage. Raw data typically refers to the information thatidentifies the image characteristics at each location within an image.For example, such image characteristics can include color, saturation,and gray-scale level.

The processor 21 can include a microcontroller, CPU, or logic unit tocontrol operation of the display device 40. The conditioning hardware 52may include amplifiers and filters for transmitting signals to thespeaker 45, and for receiving signals from the microphone 46. Theconditioning hardware 52 may be discrete components within the displaydevice 40, or may be incorporated within the processor 21 or othercomponents.

The driver controller 29 can take the raw image data generated by theprocessor 21 either directly from the processor 21 or from the framebuffer 28 and can re-format the raw image data appropriately for highspeed transmission to the array driver 22. In some implementations, thedriver controller 29 can re-format the raw image data into a data flowhaving a raster-like format, such that it has a time order suitable forscanning across the display array 30. Then the driver controller 29sends the formatted information to the array driver 22. Although adriver controller 29, such as an LCD controller, is often associatedwith the system processor 21 as a stand-alone Integrated Circuit (IC),such controllers may be implemented in many ways. For example,controllers may be embedded in the processor 21 as hardware, embedded inthe processor 21 as software, or fully integrated in hardware with thearray driver 22.

The array driver 22 can receive the formatted information from thedriver controller 29 and can re-format the video data into a parallelset of waveforms that are applied many times per second to the hundreds,and sometimes thousands (or more), of leads coming from the display'sx-y matrix of pixels.

In some implementations, the driver controller 29, the array driver 22,and the display array 30 are appropriate for any of the types ofdisplays described herein. For example, the driver controller 29 can bea conventional display controller or a bi-stable display controller(such as an IMOD controller). Additionally, the array driver 22 can be aconventional driver or a bi-stable display driver (such as an IMODdisplay driver). Moreover, the display array 30 can be a conventionaldisplay array or a bi-stable display array (such as a display includingan array of IMODs). In some implementations, the driver controller 29can be integrated with the array driver 22. Such an implementation canbe useful in highly integrated systems, for example, mobile phones,portable-electronic devices, watches or other small-area displays.

In some implementations, the input device 48 can be configured to allow,for example, a user to control the operation of the display device 40.The input device 48 can include a keypad, such as a QWERTY keyboard or atelephone keypad, a button, a switch, a rocker, a touch-sensitivescreen, a touch-sensitive screen integrated with the display array 30,or a pressure- or heat-sensitive membrane. The microphone 46 can beconfigured as an input device for the display device 40. In someimplementations, voice commands through the microphone 46 can be usedfor controlling operations of the display device 40.

The power supply 50 can include a variety of energy storage devices. Forexample, the power supply 50 may include a rechargeable battery, such asa nickel-cadmium battery or a lithium-ion battery. In implementationsusing a rechargeable battery, the rechargeable battery may be chargeableusing power coming from, for example, a wall socket of a photovoltaicdevice or array. Alternatively, the rechargeable battery can bewirelessly chargeable. The power supply 50 also can include a renewableenergy source, a capacitor, or a solar cell, including a plastic solarcell or solar-cell paint. The power supply 50 also can be configured toreceive power from a wall outlet.

In some implementations, control programmability resides in the drivercontroller 29 which can be located in several places in the electronicdisplay system. In some other implementations, control programmabilityresides in the array driver 22. The above-described optimization may beimplemented in any number of hardware and/or software components and invarious configurations. The various illustrative logics, logical blocks,modules, circuits and algorithm steps described in connection with theimplementations disclosed herein may be implemented as electronichardware, computer software, or combinations of both. Theinterchangeability of hardware and software has been describedgenerally, in terms of functionality, and illustrated in the variousillustrative components, blocks, modules, circuits and steps describedabove. Whether such functionality is implemented in hardware or softwaredepends upon the particular application and design constraints imposedon the overall system.

The hardware and data processing apparatus used to implement the variousillustrative logics, logical blocks, modules and circuits described inconnection with the aspects disclosed herein may be implemented orperformed with a general purpose single- or multi-chip processor, adigital signal processor (DSP), an application specific integratedcircuit (ASIC), a field programmable gate array (FPGA) or otherprogrammable logic device, discrete gate or transistor logic, discretehardware components, or any combination thereof designed to perform thefunctions described herein. A general purpose processor may be amicroprocessor, or, any conventional processor, controller,microcontroller, or state machine. A processor also may be implementedas a combination of computing devices, such as a combination of a DSPand a microprocessor, a plurality of microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration. In some implementations, particular steps and methods maybe performed by circuitry that is specific to a given function.

In one or more aspects, the functions described may be implemented inhardware, digital electronic circuitry, computer software, firmware,including the structures disclosed in this specification and theirstructural equivalents thereof, or in any combination thereof.Implementations of the subject matter described in this specificationalso can be implemented as one or more computer programs, i.e., one ormore modules of computer program instructions, encoded on a computerstorage media for execution by, or to control the operation of, dataprocessing apparatus.

If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. The steps of a method or algorithm disclosedherein may be implemented in a processor-executable software modulewhich may reside on a computer-readable medium. Computer-readable mediaincludes both computer storage media and communication media includingany medium that can be enabled to transfer a computer program from oneplace to another. A storage media may be any available media that may beaccessed by a computer. By way of example, and not limitation, suchcomputer-readable media may include RAM, ROM, EEPROM, CD-ROM or otheroptical disk storage, magnetic disk storage or other magnetic storagedevices, or any other medium that may be used to store desired programcode in the form of instructions or data structures and that may beaccessed by a computer. Also, any connection can be properly termed acomputer-readable medium. Disk and disc, as used herein, includescompact disc (CD), laser disc, optical disc, digital versatile disc(DVD), floppy disk, and blu-ray disc where disks usually reproduce datamagnetically, while discs reproduce data optically with lasers.Combinations of the above also may be included within the scope ofcomputer-readable media. Additionally, the operations of a method oralgorithm may reside as one or any combination or set of codes andinstructions on a machine readable medium and computer-readable medium,which may be incorporated into a computer program product.

Various modifications to the implementations described in thisdisclosure may be readily apparent to those skilled in the art, and thegeneric principles defined herein may be applied to otherimplementations without departing from the spirit or scope of thisdisclosure. Thus, the claims are not intended to be limited to theimplementations shown herein, but are to be accorded the widest scopeconsistent with this disclosure, the principles and the novel featuresdisclosed herein. The word “exemplary” is used exclusively herein tomean “serving as an example, instance, or illustration.” Anyimplementation described herein as “exemplary” is not necessarily to beconstrued as preferred or advantageous over other possibilities orimplementations. Additionally, a person having ordinary skill in the artwill readily appreciate, the terms “upper” and “lower” are sometimesused for ease of describing the figures, and indicate relative positionscorresponding to the orientation of the figure on a properly orientedpage, and may not reflect the proper orientation of an IMOD asimplemented.

Certain features that are described in this specification in the contextof separate implementations also can be implemented in combination in asingle implementation. Conversely, various features that are describedin the context of a single implementation also can be implemented inmultiple implementations separately or in any suitable subcombination.Moreover, although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, a person having ordinary skill in the art will readily recognizethat such operations need not be performed in the particular order shownor in sequential order, or that all illustrated operations be performed,to achieve desirable results. Further, the drawings may schematicallydepict one more example processes in the form of a flow diagram.However, other operations that are not depicted can be incorporated inthe example processes that are schematically illustrated. For example,one or more additional operations can be performed before, after,simultaneously, or between any of the illustrated operations. In certaincircumstances, multitasking and parallel processing may be advantageous.Moreover, the separation of various system components in theimplementations described above should not be understood as requiringsuch separation in all implementations, and it should be understood thatthe described program components and systems can generally be integratedtogether in a single software product or packaged into multiple softwareproducts. Additionally, other implementations are within the scope ofthe following claims. In some cases, the actions recited in the claimscan be performed in a different order and still achieve desirableresults.

1. A method, comprising: depositing a first layer of substantiallytransparent conductive material on a first substantially transparentsubstrate, wherein depositing the first layer involves forming a firstplurality of substantially transparent electrodes in a first region ofthe first substrate and forming a second plurality of substantiallytransparent electrodes in a second region of the first substrate;forming a layer of resistive material on the first layer ofsubstantially transparent conductive material, wherein the formingincludes forming a first plurality of resistors on some, but not all, ofthe first plurality of electrodes and forming a second plurality ofresistors on the second plurality of electrodes; depositing a secondlayer of substantially transparent conductive material on a secondsubstantially transparent and flexible substrate, wherein depositing thesecond layer involves forming a third plurality of substantiallytransparent electrodes in a first region of the second substrate andforming a fourth plurality of substantially transparent electrodes in asecond region of the second substrate with a pitch that is substantiallythe same as that of the second plurality of electrodes; forming asubstantially transparent elastomeric material in the first region ofthe first substrate; and attaching the second substrate to theelastomeric material.
 2. The method of claim 1, further includingforming a force-sensitive resistor material between the second pluralityof electrodes and the fourth plurality of electrodes.
 3. The method ofclaim 1, wherein a first index of refraction of the first substratesubstantially matches a second index of refraction of the elastomericmaterial.
 4. The method of claim 1, wherein an index of refraction ofthe elastomeric material substantially matches an index of refraction ofthe second substrate.
 5. The method of claim 1, wherein a modulus ofelasticity of the elastomeric material is substantially lower than amodulus of elasticity of the first substrate.
 6. The method of claim 1,further including forming the elastomeric material on the firstelectrodes having the first plurality of resistors deposited thereon. 7.The method of claim 1, further including forming the elastomericmaterial on the first electrodes not having the first plurality ofresistors deposited thereon.
 8. The method of claim 1, further includingforming a force-sensitive resistor material between the first pluralityof electrodes and the third plurality of electrodes.
 9. The method ofclaim 1, further including attaching the first substantially transparentsubstrate to a display device.
 10. The method of claim 1, furtherincluding configuring a sensor control system for communication with thefirst and third pluralities of substantially transparent electrodes. 11.The method of claim 1, wherein at least the depositing involves aroll-to-roll manufacturing process.
 12. The method of claim 1, furtherincluding applying an adhesive layer to the elastomeric material, butnot to the resistive material, prior to the attaching process.
 13. Themethod of claim 6, wherein forming the elastomeric material on the firstelectrodes having the first plurality of resistors deposited thereoninvolves forming the elastomeric material on the first electrodes nothaving the first plurality of resistors deposited thereon, furtherincluding removing the elastomeric material from the first electrodeshaving the first plurality of resistors deposited thereon.
 14. Themethod of claim 10, further including configuring the sensor controlsystem for communication with the second and fourth pluralities ofsubstantially transparent electrodes.
 15. The method of claim 10,further including configuring the sensor control system forcommunication with a processor of a display device.
 16. The method ofclaim 10, further including configuring the sensor control system forprocessing handwriting and touch sensor data according to electricalsignals received from the first and third pluralities of substantiallytransparent electrodes.
 17. The method of claim 13, wherein the removinginvolves removing the elastomeric material from less than 5% of thefirst region.
 18. The method of claim 14, further including configuringthe sensor control system for processing fingerprint sensor dataaccording to electrical signals received from the second and fourthpluralities of substantially transparent electrodes.
 19. The method ofclaim 16, wherein configuring the sensor control system for processinghandwriting and touch sensor data involves configuring the sensorcontrol system for projected capacitive touch sensing.
 20. The method ofclaim 16, wherein configuring the sensor control system for processinghandwriting and touch sensor data involves configuring the sensorcontrol system for resistive handwriting sensing.
 21. The method ofclaim 16, wherein configuring the sensor control system for processinghandwriting and touch sensor data involves configuring the sensorcontrol system for capacitive handwriting sensing.
 22. A method,comprising: depositing a first layer of substantially transparentconductive material on a first substantially transparent substrate,wherein depositing the first layer involves forming a first plurality ofsubstantially transparent electrodes in a first region of the firstsubstrate and forming a second plurality of substantially transparentelectrodes in a second region of the first substrate, the secondplurality of electrodes being spaced more closely than the firstplurality of electrodes; forming a layer of resistive material on thefirst layer of substantially transparent conductive material, whereinthe forming includes forming a first plurality of resistors on some, butnot all, of the first plurality of electrodes and forming a secondplurality of resistors on the second plurality of electrodes; depositinga second layer of substantially transparent conductive material on asecond substantially transparent and flexible substrate, whereindepositing the second layer involves forming a third plurality ofsubstantially transparent electrodes in a first region of the secondsubstrate and forming a fourth plurality of substantially transparentelectrodes in a second region of the second substrate with a pitch thatis substantially the same as that of the second plurality of electrodes;forming a substantially transparent elastomeric material in the firstregion of the first substrate; and attaching the second substrate to theelastomeric material.
 23. The method of claim 22, wherein an index ofrefraction of the first substrate substantially matches an index ofrefraction of the elastomeric material.
 24. The method of claim 22,wherein a modulus of elasticity of the elastomeric material issubstantially lower than a modulus of elasticity of the first substrate.25. The method of claim 22, wherein forming the substantiallytransparent elastomeric material involves substantially filling a spacebetween only a portion of the first plurality of electrodes and thethird plurality of electrodes with the elastomeric material.
 26. Themethod of claim 22, wherein forming the substantially transparentelastomeric material involves substantially filling a space betweensubstantially all of the first plurality of electrodes and the thirdplurality of electrodes with the elastomeric material.
 27. The method ofclaim 22, further including forming substantially transparent andforce-sensitive resistor material extending from the second plurality ofelectrodes to the fourth plurality of electrodes.
 28. The method ofclaim 23, wherein the index of refraction of the elastomeric materialsubstantially matches an index of refraction of the second substrate.29. The method of claim 24, wherein the modulus of elasticity of theelastomeric material is between about 0.5 and 50 megapascals.
 30. Themethod of claim 24, wherein the modulus of elasticity of the firstsubstrate is between about 0.5 and 5.0 gigapascals.